2008 APS March Meeting New Orleans, Louisiana

2008 APS March Meeting New Orleans, Louisiana http://www.aps.org/meetings/march/index.cfm

i Monday, March 10, 2008 8:00AM - 11:00AM — Session A26 DCP: Focus Session: Photophysics of Cold Molecules I Morial Convention Center 218

8:00AM A26.00001 Isolation of Molecules in Helium Nanodroplets: Spectroscopy and Dynam- ics at Ultra-cold Temperatures FRANK STIENKEMEIER, University of Freiburg — The isolation of atoms, molecules, clusters or nano-sized complexes in helium nanodroplets allows detailed spectroscopic studies at temperatures in the millikelvin range. Moreover, femtosecond real-time spectroscopy has been introduced to study dynamical processes in the ultracold helium environment. On the one hand, wave packet propagation opens a window to dynamical processes, allowing even a view to superfluid properties at the nanoscale. This is exemplified at decoherence effects in the wave packet propargation of small molecules attached to the droplets. On the other hand, high-resolution mass spectra using both femtosecond photoionisation (PI) as well as electron impact ionization enable us to characterize reactive processes at temperatures in the millikelvin range. As an example, alkali cluster – water complexes are formed in helium droplets. By recording multi-photon PI spectra we can distinguish between reactive processes of the neutral clusters and ionic reactions occurring after ionisation of the alkali cluster component. These studies pave the way to time-resolved reaction dynamics at very low temperatures.

8:36AM A26.00002 Nonequilibrium magnesium complexes formed in helium nanodroplets , JOSEF TIGGESBAUMKER,¨ ANDREAS PRZYSTAWIK, SEBASTIAN GODE,¨ KARL-HEINZ MEIWES-BROER, Institute of Physics, University of Rostock, 18051 Rostock, Germany — Doping helium droplets with alkaline earth atoms is an interesting tool to investigate the interaction with the superfluid helium. Magnesium is a corner case regarding the degree of solvation in helium [1,2] which may enable the detection of quantized vortices in helium droplets. In this contribution we add another facet to the discussion. The absorption of helium droplets doped with magnesium atoms is measured with resonant two-photon ionization at different combinations of droplet size and the number of doped Mg atoms. This enables the unambiguous identification of the absorption of an isolated atom inside the droplet centered around 279 nm. When increasing the Mg content of the droplet we find evidence for the formation of metastable, weakly bound Mg complexes. After excitation of such a complex it collapses to a Mg cluster on a timescale of 20 ps. [1] J. Reho et al., J. Chem. Phys. 112, 8409 (2000) [2] Y. Ren and V.V. Kresin, Phys. Rev. A 76, 043204 (2007)

4 8:48AM A26.00003 Superfluid He density functional theory in 2-D cylindrical coordinates1 , JUSSI ELORANTA, SEAN FRENCH, Department of Chemistry and Biochemistry, California State University at Northridge, STEVEN FIEDLER, Department of Chemical Engineering, The University of Michigan — Bosonic density functional theory describing superfluid 4He is formulated in 2-D cylindrical coordinates and a numerical implementation of the model using a regular spatial grid basis is presented. The 2-D formulation has many important applications as the 1-D treatment cannot, for example, describe translational motion of atoms and molecules solvated in the liquid and the 3-D theory is usually computationally too expensive, especially when describing dynamics in bulk superfluid 4He. The theory is implemented in both real and imaginary time forms for allowing solution of both time-dependent and time-independent problems. Two test cases for the developed method are presented and the results are compared against the previously published results. Finally, the method is applied to describe solvation of single wall carbon nanotubes in superfluid 4He at 0 K and the implications of the results to dynamic liquid response are discussed.

1Support from Research Corporation is acknowledged.

9:00AM A26.00004 Photo-induced isomerization and chemical reaction dynamics in superfluid helium droplets , JEREMY MERRITT, GARY DOUBERLY, ROGER MILLER, University of North Carolina-Chapel Hill — Near threshold photo- induced isomerization and photo-induced chemical reactions have long been sough after as sensitive probes of the underlying potential energy surface. One of the most important questions asked is how the initially bright quantum state couples to the reaction coordinate, and thus relates to energy transfer in general. Helium droplets have now allowed us to stabilize entrance channel clusters behind very small reaction barriers such that vibrational excitation may result in reaction. Through two examples, namely the isomerization of the 2 binary complexes of HF-HCN {Douberly et al. PCCP 2005, 7,463}, and the induced reaction of the gallium-HCN complex {Merritt et al. JPCA 2007, DOI:10.1021/jp074981e} we will show how the branching ratios for reaction and predissociation can determined and the influence of the superfluid He solvent.

9:12AM A26.00005 Rydberg States of Na-doped Helium Nanodroplets , MARCEL DRABBELS — The dynamics of excited states of Na atoms deposited on the surface of helium nanodroplets has been investigated with velocity map ion imaging, photoelectron spectroscopy and time-of-ﬂight mass-spectroscopy. For the ﬁrst time, the excitation spectra of Na-doped helium nanodroplets corresponding to Rydberg states of Na atoms have been measured from the lowest excited 3p state up to the ionization threshold. All lines in the excitation spectra are shifted and broadened with respect to the corresponding atomic lines. In addition to bare Na* atoms also Na*HeN (N = 1-6) exciplexes are detected upon excitation. Photoelectron spectroscopy reveals the desorption of Na* not only in the initially excited states but also in lower lying states, indicating that relaxation plays an important role. The recorded velocity distributions show interesting characteristics: for the lowest states the mean kinetic energy of Na* increases linearly with excitation energy. The velocity distributions of Na*HeN exciplexes do not manifest such remarkable properties. The observations can be largely explained by assuming that the interaction of Na* with the helium nanodroplet can be described by the sum of Na*-He pair potentials.

9:24AM A26.00006 Photoelectron imaging of doped helium nanodroplets , DANIEL NEUMARK, University of California, Berkeley — Photoelectron images of helium nanodroplets doped with Kr and Ne atoms are reported. The images and resulting photoelectron spectra were obtained using tunable synchrotron radiation to ionize the droplets. Droplets were excited at 21.6 eV, corresponding to a strong droplet electronic excitation. The rare gas dopant is then ionized via a Penning excitation transfer process. The electron kinetic energy distributions reﬂect complex ionization and electron escape dynamics.

9:36AM A26.00007 High Resolution Fluorescence Excitation and Dispersed Emission Spectra of Organic Molecules in Superfluid Helium Nanodroplets1 , ALKWIN SLENCZKA, RICARDA RIECHERS, DOMINIK PENTLEHNER, ALEXANDER VDOVIN, Institue for Physical and Theoretical Chemistry, University of Regensburg — Superfluid helium droplets serve as a very gentle cryogenic matrix for molecular spectroscopy. The low temperature and high thermal conductivity of superfluid helium droplets are of great advantage for the investigation of dispersed emission spectra of molecules. As a complement to the fluorescence excitation spectrum the emission spectra provide important details on dynamic processes of intramolecular as well as intermolecular nature. This will be demonstrated for various examples such as intramolecular proton tunnelling, isomeric van der Waals complexes, tautomerization and microsolvation.

1A Humboldt fellowship for A.V. is gratefully acknowledged 9:48AM A26.00008 Coherent boson dynamics in strongly localized potentials - helium excitations at planar aromatic molecules and trapped cold atoms , K. BIRGITTA WHALEY, University of California, Berkeley — Planar aromatic molecules provide strongly localizing potentials for helium that considerably modify the local superfluid properties of a solvating helium environment. I shall describe some of the effects of these interactions on the solvation structure and spectroscopy of tetracene and phthalocyanine in helium droplets, comparing results of zero and finite temperature quantum Monte Carlo simulations with experimental data. The helium atoms closest to the molecule are seen to show similarities to trapped cold atoms in multi-well potentials. Studies of cold bosons with attractive and repulsive interactions in double well potentials will also be presented, showing formation of squeezed and quantum superposition states of cold atoms.

10:24AM A26.00009 Fragmentation dynamics inside helium nanodroplets: new theoretical results , NADINE HALBERSTADT1, LCAR-IRSAMC, CNRS and Universite Toulouse, DAVID BONHOMMEAU2, University of Minnesota, MARIUS LEWERENZ3, Universite Paris Est, Laboratoire de Chimie Theorique — We present a theoretical study on the effect of a helium nanodroplet environment on the fragmentation dynamics of embedded rare gas cluster ions. The helium atoms are treated explicitly, with zero-point effects taken into account through an effective helium-helium interaction potential. All the nonadiabatic effects between electronic states of the ionized rare gas cluster are taken into account. Our results reveal new mechanisms for the cooling by helium, and show that the dopant can be ejected from the helium droplet. These results will be presented and discussed.

1118 route de Narbonne, 31062 Toulouse CEDEX 9, France 2207 Pleasant Street S.E., 230 Smith Hall, Minneapolis, MN 55455-0431, USA 35 Bd Descartes, 77454 Marne la Vallee Cedex 2, France

10:36AM A26.00010 Suppressing the fragmentation of fragile molecules in helium nanodroplets by co-embedding with water: Possible role of the electric dipole moment1 , YANFEI REN, VITALY KRESIN, University of Southern California — When fragile molecules are embedded in liquid helium nanodroplets, electron-impact ionization usually leads to fragmentation which is as extensive as for isolated gas-phase molecules. This occurs because of the energy release accompanying charge transfer from the impurity to the He+ hole created by electron bombardment. However, in experiments with glycine, polyglycine peptide chains, and alkane hydrocarbon chains we found that if a few molecules of water are co-embedded with these molecules, the fragmentation of the latter is drastically reduced or completely eliminated. On the other hand, the fragmentation of alkanethiols remains unaffected. On the basis of these observations, it is proposed that the fragmentation “buffering” effect may correlate with the magnitude of the impurity’s electric dipole moment, which steers the migration of the ionizing He+hole through the droplet.

1Supported by NSF

10:48AM A26.00011 Path integral investigation of the electronic spectra of He-tetracene clusters , HEATHER D. WHITLEY1, Lawrence Livermore National Laboratory, Livermore, CA 94551, K. BIRGITTA WHALEY, Department of Chemistry and Kenneth S. Pitzer Center for Theoretical Chemistry, University of California, Berkeley, CA 94720 — Planar aromatic molecules (PAMs) are nanoscale precursors to bulk graphite. Their electronic spectra have been extensively studied in 4He nanodroplets and show a number of unusual spectroscopic features. We have conducted many-body quantum simulations of tetracene in He nanodroplets to probe the 1.1 cm−1 spectral splitting of the electronic origin seen for this PAM. We calculate spectral shifts and He density proﬁles via path integral quantum Monte Carlo simulations. The spectral splitting is examined using a path integral correlation function approach to determine the lowest-lying vibrational excitation frequencies for small HeN -tetracene clusters. Simulations in the S1 state of tetracene utilize a semi-empirical perturbative interaction potential for a He atom with a PAM. Results for the splitting of the electronic origin and the spectral shifts are in good agreement with experiment. Prepared by LLNL under Contract DE-AC52-07NA27344.

1Previous aﬃliation: Department of Chemistry and Kenneth S. Pitzer Center for Theoretical Chemistry, University of California, Berkeley, CA 94720

Monday, March 10, 2008 11:15AM - 2:03PM — Session B21 DCP: Focus Session: Clusters, Cluster Assemblies, Nanoscale Materials I Morial Convention Center 213 11:15AM B21.00001 Physical and chemical properties of supported, suspended and trapped clusters , UZI LANDMAN, School of Physics, Georgia Institute of Technology — Investigations of physical systems of small sizes and reduced dimensionalities, exhibiting discrete quantized energy level spectra and specific structures and morphologies, open avenues for systematic explorations of the emerging unique behavior of materials at the nanoscale, as well as of the transition from the atomic and molecular domain to the condensed phase regime. We will discuss computer simulations and accompanying experiments exhibiting emergent physical and chemical behavior at the nanoscale, focusing on several confinement configurations – free, supported and trapped clusters. These include investigations of metallic, semiconducting, superconducting [1] and mixed metal/molecular [2] suspended nanowires, recent advances in understanding the structure and catalytic activity of supported gold nanoclusters and methods for controlling their dimensionality and properties [3], strongly correlated states and formation of electron (Wigner) clusters in 2D quantum dots, and crystallization of trapped finite boson clusters [4]. [1] A. Marchenkov, Z. Dai, C. Zhang, R. N. Barnett, U. Landman, Phys. Rev. Lett. 98, 046802 (2007); A. Marchenkov, Z. Dai, B. Donehoo, R. N. Barnett, U. Landman, Nature Nanotech. 2, 481 (2007). [2] C. Zhang, R.N. Barnett, U. Landman, Phys. Rev. Lett., in press (2007). [3] U. Landman, B. Yoon, C. Zhang, U. Heiz, M. Arenz, Topics in Catal. 44, 145 (2007). [4] C. Yannouleas and U. Landman, Reports on Progress in Physics 70, 2067 (2007).

11:51AM B21.00002 Electric Dipole Moments of Neutral Sodium Clusters1 , JOHN BOWLAN, ANTHONY LIANG, WALT DE HEER, Georgia Tech, DE HEER GROUP TEAM — Recent ab initio studies have predicted large electric dipole moments in neutral Na clusters. We performed an electric deﬂection experiment on these clusters at 20 K and have found upper bounds on their dipole moments that are orders of magnitude smaller than predicted, and consistent with zero.

1Supported by the National Science Foundation. 12:03PM B21.00003 Enhanced magnetic moments of Sc, Ti and V doped Nan(n =4, 5, 6) clusters1 , J. ULISES REVELES, Department of Physics, Virginia Commonwealth University, Richmond VA, 23284, USA, KALPATARU PRADHAN, PRASENJIT SEN, Harish-Chandra Research Institute, Allahabad 211019, INDIA, SHIV N. KHANNA, Department of Physics, Virginia Commonwealth University, Richmond VA, 23284, USA — Theoretical studies on the geometry, electronic structure and spin multiplicity of Sc, Ti and V doped Nan (n = 4, 5, 6) clusters have been carried out within a gradient corrected density functional approach. Two complementary approaches including all-electron calculations on free clusters, and supercell calculations using planewave pseudopotential and projector augmented wave formalisms have been carried out. It is shown that spin magnetic moments of the transition metal atoms, the magnitude of host polarization, and the sign of the host polarization all change with the number of alkali atoms. In particular the transition metal atoms are shown to attain spin moments that are higher than their atomic values. The role of hybridization between the transition atom d-states and the alkali sp-states is highlighted to account for the evolutions in the spin moments and host polarization.

1J.U.R. acknowledges support from U. S. Air Force Oﬃce of Scientiﬁc Research grant FA9550-05-1-0186, while S.N.K. is grateful to U.S. Department of Energy Grant DE-FG02-96ER45579 for support.

12:15PM B21.00004 Structure, Growth and Optical Properties of SinOm Nanoparticles: From SiO molecules to Silicates in Circumstellar Space1 , SELVARENGAN PARANTHAMAN, ARTHUR REBER, PENEE CLAY- BORNE, SHIV KHANNA, Virginia Commonwealth University, A. WELFORD CASTLEMAN JR., Pennsylvania State University — Synergistic eﬀort combining formation of clusters in molecular beams and ﬁrst principles electronic structure studies within a gradient corrected density functional scheme are employed to examine the geometries, stability, vibrational frequencies and optical properties of SinOm clusters. It is proposed that the oxygen enrichment needed to form silicates in interstellar space, starting from SiO molecules can occur via two processes. (1) Chemically driven compositional separation in (SiO)n motifs resulting in oxygen rich and oxygen poor regions, and (2) reaction between SinOm clusters leading to oxygen richer and poorer fragments. Theoretically calculated optical and infrared spectra of SinOm clusters exhibit features observed in the extended red emissions and blue luminescence from interstellar medium indicating that the SinOm fragments could be contributing to these spectra.

1We gratefully acknowledge support from the Department of Energy (DE-FG02-02ER46009)

12:27PM B21.00005 Cage Clusters of Gold and Tin: Golden Buckyballs and Stannaspherene1 , LAI-SHENG WANG, Washington State University — Photoelectron spectroscopy (PES) yields direct electronic structure information for size-selected clusters. Combining PES with theoretical calculations has become an effective approach to obtain structural information for small and medium-sized clusters. We present − recent discoveries of two classes of cage clusters in gold and tin. Negatively charged gold clusters (Aun ) have been shown to exhibit a remarkable structural diversity from 2D structures for n = 4-12 and the pyramidal structure for n = 20. Using PES and DFT calculations, we have found that gold clusters with n = 16-18 possess unprecedented hollow cage structures. We have been able to successfully dope a variety of transition-metal atoms into the empty spaces in the golden cages, confirming their structural robustness, as well as demonstrating chemical tuning of their electronic, magnetic, and catalytic properties. Unlike carbon, the heavier congeners of the group 14 elements are not known to form hollow cage structures similar to the fullerenes. In PES studies of tin − clusters, we noted that the spectrum of Sn12 is distinctly different from that of its neighbors or its Si/Ge counterpart. This observation led to our discovery of 2− a highly symmetric and stable icosahedral Sn12 cage, for which we coined a name “stannaspherene” to describe its high symmetry and spherical pi bonding. 2− We have also shown that all transition metals including the f-block elements can be doped inside Sn12 to form a whole class of endohedral stannaspherenes, which may be used as potential building blocks for new cluster-assembled materials. In a preliminary experiment to synthesize stannaspherene in the bulk, a 4− new cluster, Pd2@Sn18 , was crystallized and characterized, suggesting all stannaspherene and endohedral stannasphernes may be fabricated in the bulk under suitable conditions.

1This research is supported by the National Science Foundation

1:03PM B21.00006 Cooperative effect between electronic and geometric structures in binary clusters of superatoms , ATSUSHI NAKAJIMA, Keio University & JST-CREST — The fabrication of cluster-assembled materials is dependent upon finding a suitable building block for a cluster that is chemically stable and that interacts weakly with other clusters of the same material. For designing the characteristics of clusters, binary systems are very important to create functionality of materials, and application of hetero-atom doping has been undertaken in the present study to two prototypes: metallic aluminum (Al) clusters and covalent silicon (Si) clusters. In particular, efforts to examine the superatom behavior involved in electronic and geometric shell closings have focused on substituting the central atom in Al12X and MSi16. Binary aluminum and silicon clusters of Al12X and MSi16 were generated by a double laser vaporization method, and the electronic and geometric stabilities for the resulting hetero-atom encapsulated clusters were examined experimentally. For aluminum-based binary superatoms of Al12X, both experimental and theoretical results show that Al12Si has high ionization energy and low electron affinity, and Al12P has low ionization energy, both with the icosahedral structure having a central Si or P atom, revealing that Al12Si and Al12P exhibit rare-gas-like and alkali superatoms, respectively. Experiments confirmed the possibility that the change in the total number of valence + − − + electrons on substitution could produce ionically bound binary superatom complexes; the binary cluster salts (Al12P) F and (Al12B) Cs . For silicon-based binary superatoms of MSi16, on the other hand, results obtained by mass spectrometry, anion photoelectron spectroscopy, and adsorption reactivity towards H2O show that the neutral cluster doped with a group-4 atom features an electronic and a geometric closing at n=16. The MSi16 cluster with a group-4 atom undergoes an electronic change in (i) the number of valence electrons when the metal atom is substituted by the neighboring metals with a group-3 or -5 atom, and in (ii) atomic radii with the substitution of the same group elements of Zr and Hf. The reactivity of a halogen atom with the MSi16 clusters reveals that VSi16F forms a superatom complex with ionic bonding.

1:39PM B21.00007 Stability and Magnetic Coupling between Mn doped Stannaspherenes , ANIL KANDALAM, GANG CHEN, PURU JENA, Virginia Commonwealth University — The discovery of carbon fullerenes has stimulated considerable interest in the 2− search of cage clusters involving not only group IV elements but also metallic systems. The recent discovery of stannaspherene, a highly stable Sn12 hollow cage cluster with a reported diameter of 6.1 A˚ has triggered a renewed interest in the search for stable endohedral cage complexes with 3d transition metal atoms as dopants. It is anticipated that these complexes may carry large magnetic moments and can be used as building blocks for novel magnetic materials. We report the first density functional theory based study of the interaction between two Mn doped stannaspherenes (Mn@Sn12) and show that Mn@Sn12 is not only highly stable and carry a magnetic moment of 5 µB , but the clusters retain their structural identity even when they interact with each other. Equally important, the magnetic coupling depends strongly on the orientation of the clusters. We believe that these new results would encourage the scientific community to explore the possibility of synthesizing novel magnetic materials with magnetic element doped Sn12 clusters as building blocks. 1:51PM B21.00008 Structural and electronic properties of chiral gold nanoclusters , IGNACIO GARZON, ITZEL SANTIZO, LUIS PEREZ, Universidad Nacional Autonoma de Mexico — Chiral structures had been found as the most stable isomers of bare and thiolate-passivated gold nanoparticles of several sizes, from density functional calculations (DFT). These results provided theoretical support for the existence of chirality in metal clusters, suggested by the intense optical activity measured from the metal-based electronic transitions of size-separated glutathione-passivated gold nanoclusters, and more recently, of penicillamine-passivated gold clusters with metal core mean diameters of 0.57, 1.1, and 1.75 nm. A further structural analysis using the Hausdorff chirality measure, as well as, a semiclassical calculation of the circular dichroism spectrum, has confirmed the existence of chirality in Au nanoparticles. In this work, the structural and electronic properties of chiral Au nanoclusters are studied by using global optimization methods combined with semiempirical many body potentials and first principles density functional calculations. In particular, we study the Au34 cluster. For this system there exists experimental evidence on the energetic stability of a chiral structure with C3 symmetry. Our calculations theoretically confirm these results, providing further evidence on the existence of chiral gold nanoclusters.

Monday, March 10, 2008 11:15AM - 2:15PM — Session B26 DCP: Focus Session: Photophysics of Cold Molecules II Morial Convention Center 218

11:15AM B26.00001 Molecular collision studies with Stark-decelerated beams , GERARD MEIJER, Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, D-14195 Berlin, Germany — Molecular scattering behaviour has generally proven difficult to study at low collision energies. We formed a molecular beam of OH radicals with a narrow velocity distribution and a tunable velocity by passing the beam through a Stark decelerator [1]. The transition probabilities for inelastic scattering of the OH radicals with Xe atoms were measured as a function of the collision energy in the range of 50 to 400 wavenumbers. The behaviour of the cross-sections for inelastic scattering near the energetic thresholds was accurately measured, and excellent agreement was obtained with cross-sections derived from coupled- channel calculations on ab initio computed potential energy surfaces [2]. For collision studies at lower energies, the decelerated beams of molecules can be loaded into a variety of traps. In these traps, electric fields are used to keep the molecules confined in a region of space where they can be studied in complete isolation from the (hot) environment. Typically, 105 state- selected molecules can be trapped for times up to several seconds at a density of 107 mol/cm3 and at a temperature of several tens of mK [3]. The long interaction time afforded by the trap has been exploited to measure the infrared radiative lifetime of vibrationally excited OH radicals, for instance, as well as to study the far-infrared optical pumping of these polar molecules due to blackbody radiation [4]. As an alternative to these traps, we have demonstrated an electrostatic storage ring for neutral molecules. In its simplest form, a storage ring is a trap in which the molecules - rather than having a minimum potential energy at a single location in space - have a minimum potential energy on a circle. To fully exploit the possibilities offered by a ring structure, it is imperative that the molecules remain in a bunch as they revolve around the ring. This ensures a high density of stored molecules, moreover, this makes it possible to inject multiple - either co-linear or counter propagating - packets into the ring without affecting the packet(s) already stored. We have recently demonstrated a prototype molecular synchrotron, which will be used as a low-energy collider for neutral molecules in the future [5]. [1] H.L. Bethlem, G. Berden, and G. Meijer, Phys. Rev. Lett. 83, (1999) 1558-1561. [2] J.J. Gilijamse, S. Hoekstra, S.Y.T. van de Meerakker, G.C. Groenenboom, and G. Meijer, Science 313, (2006) 1617-1620. [3] S.Y.T. van de Meerakker, P.H.M. Smeets, N. Vanhaecke, R.T. Jongma, and G. Meijer, Phys. Rev. Lett. 94, (2005) Artn. 023004. [4] S. Hoekstra, J.J. Gilijamse, B. Sartakov, N. Vanhaecke, L. Scharfenberg, S.Y.T. van de Meerakker, and G. Meijer, Phys. Rev. Lett. 98, (2007) Artn. 133001. [5] C.E. Heiner, D. Carty, G. Meijer, and H.L. Bethlem, Nature Physics 3, (2007) 115-118.

11:51AM B26.00002 Magnetoelectrostatic trapping of neutral OH molecules1 , BRIAN SAWYER, BEN- JAMIN STUHL, JILA/University of Colorado, BENJAMIN LEV, University of Illinois, Urbana-Champaign, MARK YEO, JILA/University of Colorado, DAJUN WANG, JUN YE, JILA/NIST/University of Colorado — Advances in cold molecule production promise to profoundly impact research on precision measurement, quantum information, and controlled chemistry. To this end, we employ a Stark decelerator to remove 99.5% of the center-of-mass kinetic energy of a supersonic beam of ground-state OH molecules. We subsequently trap a 70 mK sample of the decelerated molecules at a density of >105 cm−3 within a magnetic quadrupole whose center lies ∼1cm from the decelerator exit. Our magnetoelectrostatic trap (MET) design allows for the addition of an electric ﬁeld of variable magnitude to the trapped sample to facilitate polar-molecule collision studies. We report progress toward observation of cold collisions between samples of polar molecules.

1The authors acknowledge support from the NSF, DOE, NIST, and NRC.

12:03PM B26.00003 Photodissociation of SO2 as a way to cold atoms and molecules , LISDAT CHRISTIAN, Physikalisch-Technische Bundesanstalt, Braunschweig, Germany, OLEG BUCICOV, MARCIN NOWAK, SEBASTIAN JUNG1, EBERHARD TIE- MANN, Institute of Quantum Optics, Leibniz University Hannover, Germany — We discuss the possibility to use the photodissociation of cold SO2 molecules to produce internally and translationally cold photofragments SO and O. It is expected from our measurements of the molecular Stark effect [1] that the dissociation pathways and excess energies of the fragments are tunable by electric fields [2]. Cold SO2 molecules are produced by Stark deceleration. We have realized a Stark decelerator that is able to slow down packages SO2 in weak-field seeking levels to a few 10 m/s center of mass velocity. A Stark decelerator with 326 stages is required for this purpose, since the ratio of Stark shift to initial kinetic energy is small for SO2. The photofragments SO and O have triplet ground states, while the ground state of SO2 is diamagnetic. In combination with the photodissociation at the threshold we want to employ this constellation to accumulate fragments in a magnetic trap by dissociating SO2 as it is stopped by electric fields in the center of the trap. [1] J. Phys. B 39, S1085 (2006). [2] Phys. Rev. A 74, 040701(R) (2006).

1present address: Atomic Physics Division, NIST Gaithersburg

12:15PM B26.00004 Alternating gradient focusing and deceleration of large molecules , KIRSTIN WOHLFART, FABIAN GRATZ,¨ FRANK FILSINGER, GERARD MEIJER, JOCHEN KUPPER,¨ Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany — During the last decade, fascinating progress has been made in the spectroscopy of the “molecular building blocks of life”. Meanwhile, our group has been developing methods to decelerate neutral, polar molecules using time varying inhomogeneous electric fields. Extending these techniques to bio-molecules would allow, for instance, to increase observation times for precision spectroscopy or to separate different conformers. However, for such large molecules all states are practically high-field seeking. Therefore, alternating gradient focusing has to be applied. Here, we demonstrate the focusing and deceleration of benzonitrile (C7H5N) from a molecular beam. Benzonitrile is prototypical for large asymmetric top molecules that exhibits rich rotational structure and a high density of states. It is decelerated in its absolute ground state from 320 m/s to 289 m/s, and similar velocity changes are obtained for excited rotational states. We are setting up a longer alternating gradient decelerator, which will enable us to decelerate benzonitrile or larger molecules to much lower velocities and to thereby completely separate the decelerated packet from the rest of the beam pulse. 12:27PM B26.00005 Production and Trapping of Ultracold Polar RbCs Molecules1 , DAVID DEMILLE, Yale University — Our group has recently demonstrated the ability to assemble ultracold, polar molecules from laser-cooled atoms. We use photoassociation followed by stimulated emission pumping to produce RbCs molecules in their absolute ground state, at temperatures T ∼ 100µK. In recent work, we have moved towards the goal of accumulated large, high-density samples of ultracold RbCs. Here we present new results on the trapping and collisional properties of RbCs in levels of high vibrational excitation.

1Supported by DOE and by NSF Grants DMR0325580 and DMR065337.

1:03PM B26.00006 Multistage Zeeman deceleration of hydrogen , S.D. HOGAN, A. WIEDERKEHR, M. ANDRIST, H. SCHMUTZ, B. LAMBILLOTTE, F. MERKT, ETH Zurich, Switzerland — With the goals of: (i) performing ultra-high resolution spectroscopy with long interaction times between a cloud of cold atoms or molecules and a narrow bandwidth radiation field, and (ii) studying cold reactive collisions in which the kinetic energies and quantum states of the colliding particles may be controlled to a high degree, a multi-stage Zeeman decelerator for neutral radicals has recently been developed in our laboratory. This instrument relies on the same concept of phase stability employed in charged particle accelerators. It opens up the possibility to manipulate the translational motion of a wider range of species than has been demonstrated using other quantum-state-selective techniques such as multi-stage Stark deceleration, and applies to a very different class of species than those to which Rydberg Stark deceleration is appropriate. The results of a recent series of experiments in which we have decelerated ground state hydrogen will be presented along with progress toward three-dimensional magnetic trapping of the decelerated radicals. In these experiments magnetic fields of 1-2 T are pulsed in each of the coils which make up the decelerator for tens of microseconds, with rise and fall times shorter than 5 µs. We have characterized the decelerated part of the gas pulse and studied the effect of zero field time windows, in which electron spin flips can occur, on the deceleration process.

1:15PM B26.00007 Kinetics of Cold Molecule Production in “Kinematic” Cooling , JEFFREY KAY, KEVIN STRECKER, DAVID CHANDLER, Sandia National Laboratories — “Kinematic” cooling is a general technique by which a vast array of molecules can be translationally cooled using crossed atomic and molecular beams. The success of the technique relies primarily on the existence of an approximate mass degeneracy between the molecule to be cooled and its atomic (or molecular) collision partner. Here, we discuss factors that affect the efficiency of cold molecule production by this method, as well as schemes that may allow tunability of the velocity and temperature of the cold molecules on a fine scale.

1:27PM B26.00008 A new source for quantum optics with biomolecules and biomolecular clusters , MARKUS MARKSTEINER, PHILIPP HASLINGER, HENDRIK ULBRICHT, MARKUS ARNDT, Faculty of Physics, University Vienna — We present recent progress towards matter wave experiments with amino acids, polypeptides and large biomolecular clusters. All successful experiments on macromolecule interferometry so far, with fullerenes, fullerene derivates and large perfluoroalkyl-functionalized azobenzenes used effusive beam sources. The combination of Stark deflectometry with quantum interferometry also allowed us to create a new device for precisely measuring electric susceptibilities of large molecules in the gas phase. In order to apply quantum interference to molecules of biological interest, we have now implemented a pulsed laser desorption source. The combination of UV laser desorption into an intense noble gas jet and single-photon ionization by a VUV excimer laser (157nm) allows us to observe intense neutral jets of amino acids (e.g. Tryptophan), nucleotides (e.g. Guanin) and polypeptides ranging from tri-peptides to Gramicidin. Remarkably, we also found a new method for producing large neutral amino acid clusters, such as for instance Trp30, with masses exceeding 6000 amu: the addition of alkaline Earth salts in the desorption process leads to the inclusion of at least one metal atom per complex and is sufficient to catalyze the cluster formation process.

1:39PM B26.00009 Collisions of ultracold molecules , HANNS-CHRISTOPH NAEGERL, University of Innsbruck — In our experiments we routinely produce ultracold trapped samples of dimer molecules out of a Cs atomic gas by exploiting the atom-dimer coupling near Feshbach resonances. We explore the rich molecular structure for the Cs dimers near the atomic threshold by consecutive state transfer after initial dimer production and produce atom-dimer mixtures for which we measure the atom-dimer collisional rate as a function of magnetic field at temperatures down to 40 nK. We find resonant enhancement of this rate for sufficiently small dimer binding energies for which coupling to an Efimov trimer state is possible. We also produce pure dimer samples for which we measure the collisional loss rate. For a weakly bound molecular s-state this rate depends strongly on temperature and on the applied magnetic field. We will also discuss first results from our experiment on producing ultracold ro-vibrational ground state molecules for the case of Cs dimers and RbCs starting from weakly bound molecules which initially are produced on a Feshbach resonance.

Monday, March 10, 2008 2:30PM - 5:18PM — Session D21 DCP: Focus Session: Clusters, Cluster Assemblies, Nanoscale Materials II Morial Convention Center 213

2:30PM D21.00001 From Superatoms to Cluster Assembled Materials , A. WELFORD CASTLEMAN, JR., Penn State University — A collaborative effort with the theoretical group of S.N. Khanna at VCU has led to the concept of superatoms comprised of clusters which mimic elements of the periodic table. The latest advances will be presented which support the contention that there should be no limitation in developing a 3-D periodic table based on this idea. As the behavior of clusters can be controlled by size and composition, the superatoms offer the potential to create unique compounds with tailored properties. One of the prime objectives of current research is to lay the foundation for forming new nanoscale materials utilizing these “elements” as the building blocks. This is viewed as one of the most promising frontiers in materials research. The current status of success in this endeavor will be discussed. AWC, Jr. gratefully acknowledges the United States Air Force Office of Scientific Research, Grant #FA9550-07-1-0151, the U. S. Department of Energy, Grant No. DE-FG02-02ER46009, and the U.S. Department of the Army through a MURI Grant #W911NF-06-1-0280, for financial support of the experimental work reported herein.

3:06PM D21.00002 From Designer Clusters to Synthetic Crystalline Nano-Assemblies1 , MEICHUN QIAN, S. KHANNA, A. REBER, Dept. of Physics, Virginia Common. Univ., A. CASTLEMAN, A. SEN, A. UGRINOV, K. DAVIS, S. PEPPERNICK, M. MERRITT, Dept. of Chemistry and Physics, Penn. State Univ. — Clusters have the potential to serve as building blocks of materials, enabling the tailoring of materials with novel properties. We have recently proposed a new protocol that combines gas phase investigations to examine feasible units, theoretical investigations of energy landscapes to identify potential motifs, and synthetic chemical approaches to synthesize cluster assemblies. We had earlier applied the 3− 3− protocol to As7 based cluster assemblies. In this work, we extend our investigations to cluster assembled materials based on As11 units as building blocks. By varying the alkali cation and introducing crypts, it is possible to form materials with arsenic clusters arranged to form one dimensional chain, two dimensional layers or three dimensional lattices and X-ray studies provide information on bond lengths etc. Theoretical studies have been carried out to examine their microscopic structure and electronic properties. It will be shown that these new compounds have the tunable electronic and optical properties. The theoretical 3− 1− predictions on the As11 Crypt(K)3 and [As11Cs2] Crypt(K) are in good agreement with the experimental observations.

1Supports from US AFOSR, ARO and DOE 3:18PM D21.00003 Geometries and stabilities of Ag-doped Sin (n =1 - 13) clusters: a first- principles study1 , FENG-CHUAN CHUANG, YUN-YI HSIEH, CHIH-CHIANG HSU, MARVIN ALBAO, Department of Physics, National Sun Yat-Sen University, Kaohsiung 804, Taiwan — The structures of AgSin (n = 1 - 13) clusters are investigated using first-principles calculations. Our studies suggest that AgSin clusters with n = 7, and 10 are relatively stable isomers and that these clusters prefer to be exohedral rather than endohedral. Moreover, doping leaves the inner core structure of the clusters largely intact. Additionally, the plot of fragmentation energies as a function of silicon atoms shows that the AgSin are favored to dissociate into one Ag atom and Sin clusters. Alternative pathways exist for n > 7 (except n = 11) in which the Ag-Si cluster dissociate into a stable Si7 and a smaller fragment AgSin−7. The AgSi11 cluster dissociates into a stable Si10 and a small fragment AgSi. Lastly, our analysis indicate that doping of Ag atom significantly decreases the gaps between the highest occupied molecular orbital and the lowest unoccupied molecular orbital for n > 7. Reference: J. Chem. Phys. 127, 144313 (2007).

1This work was supported by Taiwan National Science Council under Grant No. NSC95-2112-M110-022-MY3 and NCTS. We are grateful to the National Center for High-performance Computing for computer time and facilities.

3:30PM D21.00004 Transition Metal Doped and Encapsulated ZnO Cages , MARCELA R. BELTRAN, Insituto de Investigaciones en Materiales, Universidad Nacional Autonoma de Mexico, ARTHUR REBER, SHIV N. KHANNA, Physics Department, Virginia Commonwealth University — ZnO is a wide band gap semiconductor with potentail for applications. We had earlier shown that Zn12O12, Zn15O15, Zn18O18, and Zn21O21 clusters are particularly stable and exhibit cage structures. In this work, we examine the possibility of making magnetic materials by either substituting Zn atoms by transition metal atoms or by encapsulating transition metal clusters inside the cages. Our studies are carried out within a density functional framework employing gradient corrected functionals. The studies cover all the 3d elements and examine the strength of the magnetic moment as well as the nature of the coupling between the local moments. We also present results on the coupling between the endohedral transition metal cluster and the transition metal atoms substituting for Zn atoms within the cage.

1 3:42PM D21.00005 DFT study of a carotenoid-porphyrin-C60 light-harvesting molecular triad , TUNNA BARUAH, University of Texas at El Paso — The abundance of solar energy reaching the earth presents an attractive alternative energy source. Nearly 75% of the solar energy striking the upper atmosphere reaches the earth in the form of photons of energies typically higher than 1 eV. Biological light-harvesting systems are highly efficient in utilizing the solar radiation. Bio-mimetic molecules are investigated to mimic the photosynthesis process efficiently in laboratory. We present a computational study of the process in a bio-mimetic carotenoid-porphyrin-C60 molecular triad which is about 5 nm long. The description of the photo-induced charge separation process requires accurate excited state energies and coupling between electrons and the phonons of the system. Since charge-transfer excitations create large changes in a molecular dipole moment, changes in excited-state energies due to coupling between a 5 nm molecular photovoltaic and the surroundings (solvent and spectator molecules) also has to be taken into account. A density functional theory based method including all these effects to describe the photo-induced charge separation process will be presented.

1ONR, UTEP, NSF

4:18PM D21.00006 Spin Accommodation and Reactivity of Superatoms.1 , ARTHUR REBER, Virginia Commonwealth University — We have recently discovered novel effects that may allow tuning of the reactivity of small clusters by controlling their spin excitation, electronic structure, and local geometry. These findings offer the prospect of designing novel catalysts through cluster assemblies where chosen clusters, called superatoms, serve as elemental building blocks. Taking aluminum as an example, I will present our recent findings that illustrate how reactive clusters can be made non-reactive while inert species can be made reactive by adding hydrogen atoms. These findings offer a microscopic understanding of the recent experimental reactivity studies on aluminum and aluminum-hydrogen clusters that show variable reactivity in even electron systems and rapid etching in odd electron systems. It is shown that the reactivity of even electron clusters is governed by a spin transfer, from the triplet oxygen to the cluster, that fills the spin down antibonding orbitals on oxygen. Theoretical investigations show that when the spin transfer cannot occur, the species is unreactive, and when spin accommodation is possible, more subtle effects appear. Secondly, I will examine the reactivity of aluminum clusters with simple nucleophiles such as water. The reactivity and nature of the ensuing products is wildly variable with the size and shape of the cluster. Again, the electronic structure and local coordination of the active sites allow for an understanding of changing barrier heights and resulting reactivity. This work provides a framework with which new catalysts may be designed.

1I gratefully acknowledge support from MURI grant W911NF-06-1-0280 and the Department of Energy(DE-FG02-96ER45579).

4:54PM D21.00007 Peierls distortion of endohedral atoms in clathrate I , HIDEKAZU TOMONO, KAZUO TSUMURAYA, Meiji University, Japan — The guest atom displacements in type II clathrates have been reported on experimental and theoretical points of view. The displacements are reported to be 0.6 A˚ from the cage center of the Si28 cage to the hexagonal in the hydrogen terminated double caged Si28 cluster [1]. The distortion can be expected to occur in the type I clathrate which forms with bamboo structures in the x, y, and z directions. The guest atoms show Peiels distortion when we calculate the equilibrium distances between the two Na atoms which locate at the neighboring Si24 cages in the bamboo structure using periodic density functional calculation. The binding energy between the guest atoms is −0.10 eV/Na2. We also conﬁrm the tendency of the Peierls distotion from the force directions of guest atoms in the double unit cells that contain four Na atoms in one dimension; We will propose the cohesion mechanism of the clathrates that the clathrates are precipitated states of the connecting endohedral atoms in the 14 group atoms. So are the hydroclathrates in which the guest molecules bind each other with chains. [1] H. Takenaka and K. Tsumuraya, Mater. Trans. 47, 63 (2006).

2− 1 5:06PM D21.00008 [Te2As2] : A Planar Motif with Potential for Ferromagnetism , SHIV KHANNA, ARTHUR REBER, MEICHUN QIAN, Virginia Commonwealth University, ANGEL UGRINOV, AYUSMAN SEN, Pennsylvania State University — Here we report the synthesis and crystal structure of [K(18-crown-6)]2[Te2As2], the first four-membered ring Zintl anion of elements from groups XV and XVI, isolated from 2− an ethylenediamine solution of As, K, and As2Te3 at room temperature. X-ray analysis indicates that the [Te2As2] anion has an unexpected planar rhombic structure with alternating bonds. First-principles electronic structure investigations within the density functional framework, indicate that the Te2As2K2 motif possesses a triplet ground state where the spin configuration leads to a distortion of the square geometry into rhombus structure marked by two Te-As shorter bond length pairs joined by longer bond lengths. A NICS analysis reveals that the triplet motif has a net aromatic character. Supercell calculations on the periodic solid show that the spin moments on the individual motifs order ferromagnetically thus offering the potential of an aromatic ferromagnet made of traditionally non-magnetic elements.

1We gratefully acknowledge support from the U.S. Department of the Army through MURI grant W911NF-06-1-0280, Department of Energy (DE-FG02- 96ER45579), and AFOSR (FA9550-05-1-0186).

Monday, March 10, 2008 2:30PM - 5:30PM — Session D26 DCP: Focus Session: Photophysics of Cold Molecules III Morial Convention Center 218 2:30PM D26.00001 Spectroscopy of large hydrogen clusters in He droplets and H2 droplets. , TAKAMASA MOMOSE, The University of British Columbia — Clusters of molecular hydrogen (H2) at low temperatures have been attracted much attention because of the possible superfluid phase of molecular hydrogen. Parahydrogen has been predicted to undergo Bose-Einstein condensate (BEC) and to exhibit a superfluid phase below 6 K. However, since the freezing point of H2 (14 K) is much higher than the predicted superfluid transltion temperature, the supercooling of bulk H2 system has not been achieved despite many attempts. Clusters are known to exhibit lower freezing and melting temperatures than their bulk system due to the size effect. In addition, the melting temperature may become significantly lower than the freezing temperature in such clusters, and coexistence of liquid and solid phases between the melting and freezing temperatures has been predicted theoretically. Thus, clusters of molecular hydrogen are very appealing system for the observation of possible superfluid phase of molecular hydrogen. Since superfluid is a macroscopic property, we have studied properties of hydrogen clusters with fairly large size (N = 100 − 106) by using He droplet spectroscopy. Some advantages of using droplet spectroscopy for this study include (1) cluster size can be precisely controlled by its pickup process, and (2) the temperature of clusters is well defined. Laser induced fluorescence of several molecules doped in H2 clusters showed clear evidence of non-rigidity of hydrogen clusters at 0.4 K or 4 K. We have also observed a clear difference in the LIF spectra between parahydrogen and orthohydrogen clusters. We will discuss the properties of large parahydrogen clusters from the dependence on the cluster size and concentration of orthohydrogen.

3:06PM D26.00002 Hydrogen clusters that remained fluid , KIRILL KUYANOV-PROZUMENT, ANDREY VILESOV — Para-H2 may constitute the only other superfluid besides helium. The superfluid transition temperature is predicted to be around 2 K, well below freezing of H2 at 13.8 K. Numerous attempts to supercool macroscopic H2 samples proved to be unsuccessful. Our approach includes formation of H2 clusters in a pulsed cryogenic nozzle beam expansion of a neat pH2 gas as well as X% of pH2 diluted in He and interrogation via Coherent Anti-Stokes Raman Scattering. At X −1 −1 = 2 – 100 % the frequency of the vibrational Q1(0) line in clusters remains constant at about ν = 4149.7 cm very similar to 4149.6 cm as in solid pH2 −1 and lower than in liquid pH2at 18 K (4151.9 cm ). The rotational S0(0) transition show some characteristic crystal field splitting having magnitude of about −1 6 cm . The splitting pattern is different from that in the hcp solid, suggesting different structure in solid pH2 clusters. At X ≤ 2 %, the frequency of the −1 Q1(0) line increases to about 4150.5 cm , which is consistent with that expected in the supercooled liquid. The S0(0) transition in these clusters, consisting 4 of about 5 x 10 molecules, appears as a single line at the same frequency as in liquid pH2. The temperature of these supercooled clusters is estimated to be less than about 1 K. Possible superfluidity of the clusters is discussed.

3:18PM D26.00003 Three-body interactions in liquid and solid hydrogen: Evidence from vibrational spectroscopy , ROBERT HINDE, Univ. of Tennessee — In the cryogenic low-density liquid and solid phases of H2 and D2, the H2 and D2 molecules retain good rotational and vibrational quantum numbers that characterize their internal degrees of freedom. High-resolution infrared and Raman spectroscopic experiments provide extremely sensitive probes of these degrees of freedom. We present here fully-first-principles calculations of the infrared and Raman spectra of liquid and solid H2 and D2, calculations that employ a high-quality six-dimensional coupled-cluster H2-H2 potential energy surface and quantum Monte Carlo treatments of the single-molecule translational degrees of freedom. The computed spectra agree very well with experimental results once we include three-body interactions among the molecules, interactions which we also compute using coupled-cluster quantum chemical methods. We predict the vibrational spectra of liquid and solid H2 at several temperatures and densities to provide a framework for interpreting recent experiments designed to search for superfluid behavior in small H2 droplets. We also present preliminary calculations of the spectra of mixed H2/D2 solids that show how positional disorder affects the spectral line shapes in these systems.

3 3:30PM D26.00004 Rotational spectrum of small, doped He clusters , TATJANA SKRBIC, SISSA - DEM- OCRITOS (Trieste, Italy), SAVERIO MORONI, DEMOCRITOS - SISSA (Trieste, Italy), STEFANO BARONI, SISSA - DEMOCRITOS (SISSA) — In recent years, symmetry-adapted imaginary-time correlation functions have been extensively used to study the rotational spectrum of doped 4He clusters within the frame of the reptation quantum Monte Carlo method. The success of this approach relies on the choice of suitable correlation functions, whose spectral resolution is dominated by few, well separated eigenvalues of the Hamiltonian. Under these conditions, reliable excitation energies can be extracted by inverse Laplace transform. This method has been tailored for bosons, due to the positivity of the ground-state wave-function and to the distinctive scarcity of low-lying states. For suﬃciently small systems, however, the states of the discrete spectrum can be calculated in the same manner also with Fermi statistics, using appropriate generalizations of the correlation functions. We present rotational spectra for small 3He clusters doped with molecules –such as CO2 and OCS– whose eﬀective moments of inertia, in 4He clusters, feature a non-trivial dependence on the system size, with a pronounced turnaround for less than 10 atoms.

3:42PM D26.00005 Quantum melting and superfluidity of molecular hydrogen clusters , MASSIMO BONINSEGNI, University of Alberta — Clusters of parahydroge comprising between 10 and 50 molecules have been extensively studied by computer simulations based on the continuous-space Worm Algorithm, which allows one to go down to temperatures as low as a few hundredths of a K. These clusters display an intriguing interplay of liquid- and solid-like behavior as a function of both temperature and cluster size. In this sense, their physics is far richer than that of helium clusters. An intriguing phenomenon predicted by our simulations is quantum melting, whereby clusters in some size range (roughly between 22 and 30 molecules) are observed to go from rigid, solid-like, to essentially structureless and liquid-like as the temperature is lowered, due to the onset of quantum exchange cycles involving all the molecules in the cluster. At low temperature these clusters turn superfluid; their local superfluid response has been analyzed, and found to be essentially uniform throughout the system in the T → 0 limit, even in clusters with a pronounced shell structure. In particular, exchanges involving molecules in the inner and outer shells are shown to be underlying the superfluid response. This system can also allow one to gain insight into the relationship of the superfluid properties with Bose condensation, and aspect that has been thoroughly investigated.

4:18PM D26.00006 Alkaline Earth Metal Atom Complexes with HCN Trapped On/In Helium Droplets: Vibrational Excitation Induced Solvation and Desolvation , GARY DOUBERLY, University of Georgia — Infrared laser spectroscopy is used to probe the rotational dynamics of the binary HCN-M (M=Ca, Sr) complexes, either solvated within or bound to helium droplets. The “surface bound” spectral signatures reported previously for the HCN-alkali atom complexes are observed for both species, while a second band is observed for HCN-Ca that corresponds to a solvated species. IR-IR double resonance spectroscopy is used to probe the interconversion of the two distinct HCN-Ca populations. Above a threshold droplet size, vibrational excitation results in the solvation of the surface bound HCN-Sr complex.

4:30PM D26.00007 Imaging Photoelectron Dynamics in Doped Helium Droplets , CHIA WANG, University of California, Berkeley, OLEG KORNILOV, Lawrence Berkeley Nat’l Lab, DARCY PETERKA, JEONG KIM, OLIVER GESSNER, Lawrence Berkeley Nat’l Lab, DANIEL NEUMARK, University of California, Berkeley — Photoionization of He droplets doped with Xe and Kr atoms have been investigated by photoelectron imaging utilizing VUV synchrotron radiation. Photoelectron images were recorded over a wide range of He droplet sizes, photon energies, and dopant pick-up conditions. Signiﬁcant ionization of dopants was observed at 21.6 eV, the absorption maximum of 21P electronic excited state of He droplets, suggesting an indirect ionization via excitation transfer. Photoelectron images and spectra indicate multiple pathways for photoelectrons generated by this process to escape the droplet. Special attention is paid to the excitation transfer dynamics and the electron relaxation in He droplets. It is found that excitation transfer from 21P state to dopants competes with relaxation to the lower 21S state. The excitation is likely a localized exciton that transfers the energy to the dopant via a dipole-dipole hopping mechanism. The conduction band of He droplets as a function of droplet size is also observed. The conduction band edge reaches the bulk limit for the largest He droplets. The electron under the conduction band becomes trapped and forms an electron bubble that escapes the droplet by transcending a barrier near the liquid/vapor interface. 4:42PM D26.00008 Interchange-Tunneling Splitting in HCl Dimer in Helium Nanodroplets , DMITRY SKVORTSOV, RUSSELL SLITER, Univ of Southern California, MYONG YONG CHOI1, Gyeongsang National University, ANDREY F. VILESOV, Univ of Southern California — Infrared spectra of HCl dimers have been obtained in helium nanodroplets. The splitting in the vibrationally excited state of the 35 37 −1 −1 bonded H-Cl stretching band (v2) in (H Cl - H Cl) dimers was obtained to be 2.7 cm as compared to 3.7 cm in free dimer. From the splitting, the strength of the interchange-tunneling interaction in liquid helium was obtained to be 0.85 cm−1, which is about a factor of two smaller than in the free dimer. The results are compared with the previous spectroscopic study of (HF)2 in He droplets as well as to the theoretical study of (HF)2 and (HCl)2 dimers in small He clusters.

1Gyeongsang National University, Jinju, 660-701, South Korea

4 4:54PM D26.00009 Path integral studies of methane rotations in He clusters1 , NIKOLAY MARKOVSKIY, CHI MAK, University of Southern California — Path integral simulations have been carried out to study the rotations of a methane inside a single shell of 4He atoms at 0.3 K to address the question of whether dopant molecule rotations can be used to probe the quantum statistics and superfluidity of the shell. We examined the effects of the probe molecule on the 4He exchanges and their counter effects on the renormalized rotation constant of the probe systematically by varying the intrinsic moment of inertia of the methane. The observed effects show strong dependence on the intrinsic moment of inertia of the rotating probe, with a heavy probe favoring stronger templating of the 4He density and a corresponding suppression of exchanges in the shell, as well as a large renormalization in the probe’s effective rotation constant, while a light probe shows almost no effect on the shell density or the effective rotation constant. These results can be rationalized in terms of a rotational smearing effect and suggest that there is no clearly quantifiable relationship between the superfluid fraction of the shell and the renormalized rotation constant of the probe for cases where the probe molecule has weak anisotropic interactions with the 4He atoms.

1National Science Foundation

1 5:06PM D26.00010 Pump-probe spectroscopy of Rg-Br2 linear isomers , JORDAN PIO, CRAIG BIELER, WYTZE VAN DER VEER, KENNETH JANDA, University of California-Irvine — We have recorded and analyzed the X →B spectra for three Rg–Br-Br linear isomers [Rg = He, Ne, Ar] using pump-probe spectroscopy. This work is an interesting test case for the transition from quantum to quasi-classical dynamics, and how the dynamics are interconnected with changes in the potential energy surface. Helium is not only much lighter than argon, but the He-Br2 potential well is much shallower than that of Ar-Br2. Excitation spectra to individual Rg-Br2 (B, ν’) intermolecular potentials were recorded by probing the Br2 (B, ν’) asymptotic limit of the potential while scanning the pump laser. The continuum spectra of the three species are very diﬀerent, with the He-Br2 spectrum peaking −1 at threshold while the Ar-Br2 spectrum is negligible at threshold and strongly blue shifted. The linear Ne-Br2 bond energy was measured to be 71 ± 3 cm by the threshold energy for the onset of the continuum. Since excitation tends to move electron density to the σ∗ orbital of the Br-Br bond near the rare gas atom, the intramolecular stretching vibration (Br-Br) and the intermolecular stretching vibration (Rg-Br) are strongly coupled. The experiments will be compared to a two dimensional model using the best available potential energy functions.

1Supported by NSF Award Nos. CHE-0213149 and CHE-0404743.

5:18PM D26.00011 Time-resolved photoionization of He droplets using high-harmonic , OLEG KORNILOV, Lawrence Berkeley Laboratory, UC Berkeley, OLIVER GESSNER, MATHEW LEONARD, STEPHEN LEONE, DANIEL NEUMARK, CHUN-TE PENG, CHIA WANG — Helium droplets are widely used as nanocontainers for matrix-isolated rotational, vibrational and electronic spectroscopy. Their superﬂuid nature and low temperatures (0.37K) provide gentle environment for embedded atoms, molecules and complexes. However, most of the traditional spectroscopic techniques are not eﬃcient for pure droplets, because of the very high energies of electronic transitions. One of the recent studies [1] conducted using synchrotron light demonstrated very interesting phenomena in photoionization of pure He droplets. It has been shown that below the threshold for He atom photoionization essentially zero kinetic energy electrons are emitted independent of the wavelength of the photoionizing radiation. In this contribution a new experiment will be presented utilizing a novel source of VUV radiation based on the high-harmonic generation. In this process femtosecond pulses of radiation are created, which will be used in a VUV-pump/IR-probe scheme to study dynamics of photoionization of He droplets. First results towards the time-dependent photoelectron spectra will be presented. [1] D. Peterka et al, Phys. Rev. Lett. 91, 043401 (2003)

Tuesday, March 11, 2008 8:00AM - 10:48AM — Session H21 DCP: Focus Session: Clusters, Cluster Assemblies, Nanoscale Materials III Morial Convention Center 213 8:00AM H21.00001 Probing electronic and magnetic properties of atomic and molecular clusters with sharp tips1 , JEAN-PIERRE BUCHER, UniversitéLouis Pasteur, Institut de Physique et Chimie des Matériaux de Strasbourg — Probing magnetic and transport properties on a local basis with the tip of a scanning tunneling microscope (STM) allows establishing close links with the exciting field of magnetic read and write processes. Some examples of applications of this approach to magnetic nanostructures will be shown. First of all, the fundamental properties of Co nanoclusters, on metal surfaces will be presented. These clusters have been probed by low temperature dI/dV spectroscopy (STS). It is found that occupied electronic surface states of the Co clusters are sensitive to the crystallographic stacking and furthermore exhibit a downward energy shift as the cluster size decreases. Ab initio calculations confirm that the observed shift is due to the size dependent mesoscopic relaxation in the clusters. When a magnetic tip is used in low temperature spin polarized (SP)-STM experiment, it is possible to reveal spin polarized feature in the local density of states. For example, one is able to identify two magnetization states of the nanometer Co clusters, corresponding to the parallel or antiparallel configuration with respect to the tip polarization. Progress in the emerging field of spintronics strongly relies on the fundamental understanding of electron/spin transport and magnetic phenomena in reduced dimensions, down to the extreme limit of individual molecules, or even single atoms where sizeable quantum effects are expected. Electronic and magnetic properties of Co atoms and metal-based molecular magnets adsorbed on magnetic nano-islands or on non magnetic surfaces will be presented. On the example of Co-phtalocyanines prepared in UHV at 4.6 K, it will be shown that dI/dV characteristics are representative of both, the nature of the molecule and also its interaction with the substrate.

1Support from the MAGMANet network of excellence of the European Community is greatly acknowledged.

8:36AM H21.00002 First Principles Theory of Supported Clusters with Complex Magnetic Order. , OLLE ERIKSSON, Uppsala University — It is demonstrated that the magnetic interactions can be drastically different for nano-sized systems compared to those of bulk or surfaces. In a real-space formalism we have developed a technique to calculate non-collinear magnetization structures and hence exchange interactions. Our results for magnetic Cr, Mn and Fe clusters supported on a Cu(111) surface show that the magnetic ordering as a rule is non-collinear and can not always be described using a simple Heisenberg Hamiltonian. We argue that the use of ab initio calculations allowing for non-collinear coupling between atomic spins constitute an efficient and reliable way of analyzing nano-sized magnets. 9:12AM H21.00003 Magnetic properties and stability of metalloinorganic clusters1 , ROBERTO ROBLES, SHIV KHANNA, Dept. of Physics, Virginia Commonwealth University, Richmond, VA 23284 — Theoretical studies on the structure, stability, electronic structure and magnetic properties of binary clusters SinTMm (n=1-8, TM=Cr,Mn) have been carried out within a density functional formalism using the generalized gradient approximation. The stability of the clusters as a function size is analyzed in terms of several criteria, like the progression in bonding energy and HOMO-LUMO gap, with the ultimate objective of identifying the simple rules that can guide the search of stable species. The magnetic properties of the clusters are investigated by considering different ferromagnetic and antiferromagnetic arrangements of the local spin moments and optimizing the geometry and the spin state to determine the ground state including possible isomers. The possible use of these clusters as building blocks of cluster assemblies is discussed, and finally, the interest of these assemblies in the design of materials which could be used in the field of spintronics is briefly considered.

1We are grateful to U.S. Department of the Army for ﬁnancial support (MURI Grant # W911NF-06-1-0280).

9:24AM H21.00004 Intermediate valence, local antiferromagnetic coupling and the Kondo effect in ytterbium organometallic molecules , C.H. BOOTH, W.W. LUKENS, Lawrence Berkeley National Laboratory (LBNL), M.D. WALTER, D. KAZHDAN, R.A. ANDERSEN, LBNL and University of California, Berkeley, E.D. BAUER, Los Alamos National Laboratory, L. MARON, INSA Toulouse, O. EISENSTEIN, Universite Montpellier — Studying magnetic ions coupling to aromatic rings in organometallic molecules provides an analogous route to studying the Kondo effect in nanoscale systems. We extend the number of molecules displaying such effects in their magnetism and x-ray absorption spectroscopy from cerocene [Ce(C8H8)2] and Cp*2Yb(bipy) [Cp*=pentamethylcyclopentadienyl, bipy=bipyridine) to a collection of Cp*2Yb(L) molecules, where L is one of various bipyridyl or diazadiene ligands. Clear trends are observed in both the magnetic susceptibility and the Yb valence that indicate changes in the fundamental temperature scale. CASSCF calculations indicate the intermediate valence is primarily due to a configuration interaction between the open-shell f 13π∗1 and the closed-shell f 14π∗0 spin-singlet states, in direct analogy to the Kondo effect in intermetallic systems. These studies increase the range of molecular species where such properties are observed, and point toward understanding the ubiquity of such effects and their involvement in fundamental bonding and magnetism in organometallic molecules.

9:36AM H21.00005 The structure, stability, and magnetic properties of Au(111)/NiO(111) interface: density functional theory study1 , K.L. YAO, Y.L. LI, Z.L. LIU, Huazhong University of Science and Technology — We studied the electronic structure of Au(111)/NiO(111) interface in accordance with the two models of NiO(111) surface. The work of adhesion, the spin magnetic moment, the stability and the electronic properties of the Au(111)/NiO(111) interface were calculated by density functional theory (DFT). The calculated results of Au(111)/NiO(111) interface were then compared with non-polar Au(100)/NiO(100) interface. At the same time, the total density of states (DOS) of Au(111)/NiO(111) interface corresponding to the two models were also calculated. The calculations reveal that the Ni-terminated and the oxidized interfaces have antiferromagnetic properties, while the O-terminated interface exhibits ferromagnetic properties.

1This work was supported by the National Natural Science Foundation of China under Grant Nos. 10574047,10574048 and 20490210. It was also supported by National 973 project under grant No. 2006CB921600.

9:48AM H21.00006 Investigating the Molecular Level Details of Catalytic Oxidation Reactions1 , GRANT JOHNSON, Pennsylvania State University — Gas-phase cluster reactivity studies are providing significant insight into the molecular level mechanisms of oxidation reactions occurring on catalytic surfaces. Our experimental approach, employing tandem mass spectrometry, uses mass selected metal oxide clusters to model specific catalytic active sites. This technique enables investigation of the influence of factors such as size, stoichiometry, charge state, and elemental composition on the reactivity of catalytic materials. Particular emphasis is on identifying species with enhanced activity for the selective oxidation of simple hydrocarbons and atmospheric pollutants. Recent findings pertain to the kinetics of ethylene oxidation in the presence of vanadium oxides and the oxidation of carbon monoxide in the presence of gold and iron. Through a combination of experiments and theoretical calculations we establish structure-reactivity relationships and propose general reaction mechanisms for these catalytic processes.

1Financial support provided by the U. S. Department of Energy, Grant No. DE-FG02-92ER14258.

1 10:24AM H21.00007 Effect of ligand on the geometric and electronic structure of Au13 cluster , GHAZAL SHAFAI, SAMPYO HONG, TALAT RAHMAN, University of Central Florida, MASSIMO BERTINO, Virginia Commonwealth University — We have carried out calculations based on the density functional theory in the projector augmented wave scheme (PAW) and the pseudopotential approach, to examine the effect of the ligand on the geometric and electronic structure of Au13 cluster. We find bare Au13 to form a flat flake, in agreement with previous theoretical calculations. This structure is lower in energy by 2.60 eV in comparison with the well ordered icosahedron geometry. Our results show, however, that the Au13 cluster covered with ligands of phosphine (PH3) forms a stable spherical structure (icosahedron) in agreement with the experiment [1] which is by 0.08 eV lower in energy when compared to the flat-flake complex. If the phosphine is replaced by H, the spherical structure is no longer stable, but it still maintains a 3 dimensional form, signifying the effect of the ligand in stabilization of the structure. We observe a narrow d-band for flat-flake gold atoms in the complex, while in the icosahedron structure the d-band is wider. We also find a stronger overlap between the p orbitals of the P atom with d orbitals of gold atoms in the icosahedron complex. [1] M. F. Bertino et. al. Phys. Chem. B Lett. 110, 21416 (2006)

1Work supported in part by DOE grant DE-FG02-03ER46354.

10:36AM H21.00008 Superheating, Melting and Precursors to Melting in Metal Nanoparticles , DMITRI SCHEBARCHOV, Victoria University of Wellington, SHAUN HENDY, Industrial Reseach Ltd — We have investigated precursors to melting in metal nanoparticles using molecular dynamics in the microcanonical ensemble. At the onset of solid-liquid phase coexistence, we find first-order transitions in clusters with non-melting facets (i.e. facets that are not wet by the melt such as Pb (111)), and continuous transitions otherwise. In sufficiently small clusters however, we find that static solid-liquid coexistence is unstable. Further, the size at which the instability arises, and even the melting temperature, depends on the ability of the melt to wet the solid facets of the cluster. In particles with non-melting facets we show that the melting temperature can exceed that of the bulk material. Finally, we also discuss a range of solid-solid transitions that have been observed to occur during solid-liquid phase coexistence, some of which are again driven by the preference of the melt to wet certain crystal facets.

Tuesday, March 11, 2008 8:00AM - 11:00AM — Session H26 DCP: Focus Session: Photophysics of Cold Molecules IV Morial Convention Center 218 8:00AM H26.00001 Reactions of cold trapped anions , ROLAND WESTER, Physikalisches Institut, Albert-Ludwigs- Universitaet Freiburg, Hermann-Herder-Str. 3, 79104 Freiburg, Germany — Interactions of negative ions with small organic molecules represent model systems for the investigation of reaction dynamics in few-body systems. Their corrugated potential energy landscape, originating in long-range attractive and short-range repulsive forces, requires the coupling of different degrees of freedom for reactions to occur. We have adopted two complementary approaches to study anion- molecule reaction dynamics. Using velocity map imaging in combination with crossed beams at low energy we study the differential cross section of negative ion reactions. For nucleophilic substitution reactions we have observed several distinct reaction mechanisms when varying the collision energy [1]. Total reaction rate measurements, which we carry out in the box-shaped potential of a 22pole ion trap [2], have revealed unexpected temperature-dependences for proton transfer and for cluster stabilisation at low temperatures. In addition, laser-induced photodetachment is studied in the trap to obtain absolute destruction cross sections for negative ions in light fields [3]. These results are relevant for the understanding of the negative ion abundances in interstellar molecular clouds. [1] J. Mikosch et al., Science (in press) [2] J. Mikosch et al., Phys. Rev. Lett. 98, 223001 (2007) [3] S. Trippel et al., Phys. Rev. Lett. 97, 193003 (2006)

8:36AM H26.00002 Cold reactive collisions between laser-cooled ions and velocity-selected neutral molecules , MARTIN BELL, STEFAN WILLITSCH, ALEXANDER GINGELL, SIMON PROCTER, TIMOTHY SOFTLEY, Department of Chemistry, University of Oxford — The recent development of a range of techniques for producing “cold” molecules at very low translational temperatures T < 1 K in the gas phase has provided the opportunity for studying molecular collisions in a new physical regime. We report a new experimental method to study reactive collisions between ions and neutral molecules at very low temperatures which allows for tunable collision energies and a variety of chemically diverse reaction partners. Our technique relies on the combination of a quadrupole-guide velocity selector for the generation of cold polar molecules with a facility to produce strongly ordered samples of laser-cooled ions in an ion trap, usually referred to as Coulomb crystals. Despite the low ﬂuxes of neutral molecules obtained from the quadrupole-guide, the strong localization and long trapping times of the ions allows chemical reactions to be studied at the single-particle level. In + a proof-of-principle experiment, we have studied the chemical reaction between translationally cold CH3F molecules and laser-cooled Ca ions in a collision energy range corresponding to 1-10 K. The characteristics of our cold-molecule sources and the performance of the new technique as well as perspectives for further developments will be discussed.

8:48AM H26.00003 Demonstration of a three-dimensional trap for state-selected Rydberg atoms , STEPHEN HOGAN, FREDERIC MERKT, ETH Zurich, Switzerland — Recent progress in the development of methods by which to decelerate and manipulate the translational motion of Rydberg atoms and molecules in the gas phase using static and time-varying inhomogeneous electric fields has led to the experimental realization of Rydberg atom optics elements including a lens, a mirror and a two-dimensional trap. These experiments exploit the very large electric dipole moments associated with Rydberg Stark states, and have demonstrated the possibility to stop a seeded, pulsed, supersonic beam of atomic hydrogen traveling with an initial velocity of 700 ms−1 within 3 mm and 5 µs using electric fields of only a few kVcm−1. With the goal of achieving complete control of a cloud of Rydberg atoms or molecules in three-dimensions, we have recently designed and constructed a three-dimensional electrostatic trap for these particles. The design of this trap will be presented along with the results of a series of experiments in which we have used the trap to confine, in three dimensions, a cloud of atomic hydrogen Rydberg atoms in states with principal quantum numbers around n = 30. The dynamics of the Rydberg atoms in the trap have been investigated by pulsed field ionization and imaging techniques. Under favorable conditions, trapping times on the order of 150 µs have been observed, corresponding to the radiative lifetimes of the excited states.

9:00AM H26.00004 Measuring the role of alignment in a molecule optical lens , SIMON M. PURCELL, PETER F. BARKER, University College London — Far off-resonant pulsed lasers have been used to deflect and focus molecules via the optical dipole force, which is proportional the effective polarisability of the species [1]. Molecules have an anisotropic polarisability, which in the presence of an intense linearly polarised optical field (1012 Wcm−2) causes the molecule to align with the field polarisation vector. This alignment occurs due to the creation of pendular states which are a superposition of the field free rotational states of the molecule[2]. This alignment of the molecule with the electric field can result in a higher effective polarisability leading to an increased dipole force that can be used to tailor the properties of molecular optical elements. Using this property, we are studying how the field polarisation can be used to modify the focal length of the molecule optical lens, created by a focused laser beam. We will present calculations of this process and a comparison with our experiments on cold (3 K) carbon disulphide molecules focused by a Nd:YAG laser beam. [1] H.S Chung, B.S Zhao, S.H. Lee et al., J. Chem. Phys 114, 8293 (2001) [2] B. Friedrich, D. Herschbach, J. Phys. Chem. 99, 15686 (1995)

9:12AM H26.00005 Cold and ultracold polar molecules , JUN YE, JILA, NIST and Univ. of Colorado — Study of ultracold molecules promises important benefits such as novel control of chemical reactions and molecular collisions, precision measurement of fundamental physical properties, and new methods for quantum information processing and quantum simulations. We undertake two approaches aimed to produce cold, polar molecular samples. In the first approach, we work directly with ground-state polar molecules such as hydroxyl radicals (OH) or formaldehyde molecules (H2CO). After Stark deceleration through an inhomogeneously distributed electric field, OH molecules are loaded into a magnetic trap at a density ∼3 x 105 cm−3 and temperature of 50 mK. An important advantage of magnetically trapping OH molecules is the freedom in applying an external electric field without significantly affecting the trap dynamics. The open geometry of the trap will enable experimental studies of cold, dipolar collisions subject to an external electric field. We will report our latest progress towards this goal. In the second approach we explore the possibility of producing ultracold polar molecules via association of two different atoms from ultracold atom gas mixtures near quantum degeneracy. Specifically, an interspecies Feshbach resonance between bosonic 87Rb and fermionic 40K permits efficient creations of heteronuclear Feshbach molecules. Subsequent optical spectroscopy reveals promising paths to efficiently transfer populations from the weakly bound to more deeply bound states. Progress on the production of these ultracold fermionic polar molecules will be reported.

9:48AM H26.00006 Experimental demonstration of electrostatic surface guiding for cold polar molecules1 , YONG XIA, YALING YIN, JIANPING YIN, Key Laboratory of Optical and Magnetic Resonance Spectroscopy, Department of Physics,East China Normal University — We demonstrate an electrostatic surface guiding for cold polar molecules over a long distance of 44.5 cm on a substrate by using a hollow electrostatic ﬁeld, which is generated by two parallel charged wires and a grounded metal-plate. We measure the transverse spatial distribution of the guided supersonic D2O (including CH3Br) molecular beam and its longitudinal velocity one, and study the dependence of the relative guiding eﬃciency and the transverse temperature of the guided molecular beam on the guiding voltage, also perform Mote-Carlo simulations and theoretical studies for the molecular guiding process, and our guiding scheme has some potential applications in molecule optics, such as molecular-beam splitter, integrated molecular optics, etc.

1This work is supported by the Grant Nos. 10434060, 2006CB921604, 07jc14017. 10:00AM H26.00007 Rotational Spectra of Methane in Helium-4 , ROBERT ZILLICH, Kepler University, Linz, BIRGITTA WHALEY, University of California, Berkeley — We extend correlated basis function (CBF) theory, in combination with diffusion Monte Carlo simulations, to spherical top molecules solvated in superfluid 4He droplets. Similarly to our previous CBF work on linear molecules, the rotational excitations of a spherical top molecule are renormalized by a self energy which contains the 4He density modulation around the molecule as coupling. Due to the high symmetry of this density in the case of solvated spherical molecules the rotation-4He coupling turns out to be weak, and the corresponding reduction of the effective rotational constant is small. Furthermore, unlike for linear molecules, for spherical top molecules the symmetry of the gas phase rotational spectrum is not preserved. Instead, for excitations of total angular momentum J ≥ 2, we find that the self energy induces a splitting of the rotational energies. We present results for the rotational spectrum of solvated CH4 and CD4 for several available He-CH4 potential energy surfaces, and compare with experimental results measured recently. We propose to measure spectra of partially substituted methane (e.g. CDH3) to investigate the effect of symmetry breaking on the rotation-4He coupling strength.

10:12AM H26.00008 Water containing molecular complexes studied by superfluid helium droplet spectroscopy , SUSUMU KUMA, The University of British Columbia, MIKHAIL SLIPCHENKO, Iowa State University, TAKAMASA MOMOSE, The University of British Columbia, ANDREY VILESOV, University of Southern California — Superfluid helium droplets offer an ideal environment for spectroscopic studies of molecular complexes by virtue of the controllable aggregation process of embedded molecules and its weak interaction as a matrix medium. Here, we report the infrared spectroscopy of Ar-H2O, N2-H2O, and O2-H2O complexes picked up in He droplets. The observed spectra in the −1 anti-symmetric stretching vibrational region (ν3) of water around 3750 cm indicated that the water molecule in complexes rotates nearly freely in Ar-H2O and O2-H2O, while not in N2-H2O. The spectra of Ar-H2O and O2-H2O exhibited the splitting of the rotational lines, which is due to the anisotropy of their intermolecular potential. We have analyzed the observed splittings in the spectra to determine the intermolecular potentials of Ar-H2O and O2-H2O in helium droplets. These results are compared with the corresponding potentials previously studied in both experimentally and theoretically.

10:24AM H26.00009 Microwave spectroscopy of doped helium clusters and doped helium droplets , WOLFGANG JAGER,¨ University of Alberta — High resolution microwave and infrared spectroscopy of small to medium sized doped helium clusters, e.g. HeN -OCS with N from 2 to 70, has given detailed insights into how superfluidity, a bulk phase property, evolves from the microscopic scale. Some of the most significant findings were oscillatory behavior of cluster rotational constant B with number of helium atoms, N, and the observation of very narrow lines (15 kHz in microwave and 0.001 cm−1 in the infrared region), even for the largest N. How can this be reconciled with the broad (up to several GHz wide) lines of rotational and ro-vibrational transitions of molecular dopants in helium droplets? Microwave experiments of molecular dopants embedded in helium nanodroplets can help answer this question. We have measured the pure tunneling inversion transition of ammonia in helium droplets at about 20.7 GHz. A complex line shape, consisting of a sharp (15 MHz wide) line on top of a broad background (1.5 GHz wide) was observed. The line shape could be simulated by assuming identical energy sublevels of the initial and final state of the transition. This provides direct evidence for the existence of an energy level substructure of molecular states in doped helium droplets. Microwave rotational transitions of carbonylsulfide, OCS, in helium droplets show increase in line width with increasing rotational quantum number J and, in some cases, prominent fine-structures. Some of these features can be interpreted in terms of droplet size distribution.

Tuesday, March 11, 2008 11:15AM - 2:03PM — Session J21 DCP: Focus Session: Clusters, Cluster Assemblies, Nanoscale Materials IV Morial Convention Center 213 11:15AM J21.00001 Quantum Mechanics and Electrodynamics Studies of the Optical Proper- ties of Metal Clusters/Nanoparticles , GEORGE SCHATZ, Northwestern University — This talk will describe the use of electrodynamics and quantum mechanics methods to describe the optical properties of silver and gold nanoparticles and other nanostructures. This work has been done in collaboration with several experimental colleagues, including Chad Mirkin, Rick Van Duyne and Teri Odom. Our recent work has focused on the optical properties of metal nanoparticles that are coated with molecules that are detected either through their influence plasmon resonance excitation, or via surface enhanced Raman spectroscopy (SERS). Electrodynamics calculations using either the DDA or FDTD methods provide a quantitative tool for characterizing far field properties, and at a more primitive level estimates of SERS intensities. Quantum mechanics, as developed using time dependent density functional theory, is restricted to small metal clusters, but the same methods of far field spectroscopy and SERS can still be studied.

11:51AM J21.00002 Low Temperature Static Dipole Polarizability of Free Sodium Clusters with from 2 to 250 atoms , ANTHONY LIANG, JOHN BOWLAN, GaTech, XIAO- SHAN XU, SHUANGE-YE YIN, WALT A. DE HEER, GaTech — The electric dipole polarizabilities of all sodium clusters Nan were measured from the atom up to n =250 using the molecular beam deﬂection method. Clusters were formed in cryogenic laser vaporization source operating at a temperature of 20 K. This complete sequence of high-resolution polarizablities measurements greatly enhances previous measurements. Electronic shell eﬀects are observed as well as several features that are not readily understood in the shell model. The asymptotic limit of the measurements appears not to converge to the bulk sodium polarizability value. The data are compared with theoretical predictions.

12:03PM J21.00003 Novel Properties of Diamondoid Molecules , WILLIAM CLAY, ZHI LIU, WANLI YANG COLLABORATION, ZHI-XUN SHEN COLLABORATION, NICK MELOSH COLLABORATION, JEREMY DAHL COLLABORATION, ROBERT CARLSON COLLABORATION — The recent isolation of a number of diamond-like hydrocarbons molecules (diamondoids) has sparked renewed interest in these unusual molecular systems. Several unique properties of these molecules are investigated. Diamondoid monolayers have been found to profoundly alter the electron emission tail of metal substrates in recent photoemission experiments, producing a sharp, nearly monochromatic peak. It is postulated that the cause of this effect is negative electron affinity combined with a strong electron-phonon interaction. New data and simulation results are presented to support this theory. Additionally, photoluminescence spectra for a number of diamondoid crystals are presented, taken with a 229 nm laser. To our knowledge, this is the first observation of UV photoluminescence in a saturated hydrocarbon molecule. Possible explanations for this phenomenon are discussed. 12:15PM J21.00004 Room temperature stability of mass selected Ag clusters on C60 functionalized surfaces1 , STEFANIE DUFFE, LUKAS PATRYARCHA, TORSTEN RICHTER, BENEDIKT SIEBEN, HEINZ HOVEL,¨ Technische Universitaet Dortmund, Experimentelle Physik I, Germany, CHUNRONG YIN, BERND VON ISSENDORFF, Universitaet Freiburg, Fakultaet fuer Physik, Germany, MICHAEL + + MOSELER, Fraunhofer-Institut fuer Werkstoffmechanik IWM, Freiburg, Germany — Mass selected clusters from Ag55 to Ag561±5 were soft landed on HOPG and Au(111) functionalized with 1 and 2 monolayers (ML) of C60 molecules [1]. Depositions at 165 K gave extremely narrow cluster height distributions in STM images measured at 77 K. Using C60/HOPG or 2 ML C60/Au(111) the cluster heights are stable for more than 12 h at room temperature (RT). For 1 ML C60/Au(111) the cluster height decreases and finally all clusters disappear at RT. Molecular dynamics simulations reveal a process by which the clusters decay atom by atom through 1 ML C60/Au(111) at RT. A sharp maximum at 1.7 nm cluster height forms during the cluster decay, indicating that there exists some metastable ’supported magic number’. [1] S. Duffe et al., Eur. Phys. J. D (2007), published online

1Work supported by the Deutsche Forschungsgemeinschaft (SPP 1153)

12:27PM J21.00005 Modification on the melting of aluminum nanoclusters by a copper atom: − 1 heat capacities of CuAln−1 nanoalloys , BAOPENG CAO, COLLEEN M. NEAL, ANNE M. STARACE, MARTIN F. JARROLD, Department of Chemistry, Indiana University, 800 E Kirkwood Ave., Bloomington, IN 47405 — The melting of alloyclusters is currently of great interest and − emerging as an important research area. In this talk, we report the synthesis and melting transition of CuAln−1 nanoalloy clusters (n = 49 – 62). Heat capacities − and melting behaviors have been determined for CuAln−1 nanoalloy clusters using a novel collision induced dissociation method and are compared with those + of pure aluminum cluster Aln . All these nanoalloys present a first order melting transition at temperatures well-below the melting temperature of the bulk aluminum and the eutectic temperature of their bulk alloys. No eutectic characteristic is detected for these nanoalloyclusters. Upon substitution of Al with a single copper atom, the melting of pure aluminum clusters has been altered considerably. Size and charge effects of the doping atom on the melting of host nanoclusters are discussed.

1We thank the NSF for ﬁnancial support.

12:39PM J21.00006 Forces between Functionalized Silica Nanoparticles1 , J. MATTHEW D. LANE, AHMED E. ISMAIL, MICHAEL CHANDROSS, GARY S. GREST, Sandia National Labs — Polymer-coated nanoparticles have a wide variety of applications, including drug delivery, adhesives, coatings, and magnetics. Although, the complexity of these nanoparticles precludes atomistic simulations of large numbers of nanoparticles in solution, it is possible to study the interaction between pairs of nanoparticles in an explicit solvent using molecular dynamics. From these simulations, we can compute the potential of mean force (PMF) between nanoparticles, which can be used in coarse-grained simulations at larger length and time scales. In particular, we present results for PMFs between polymer-grafted silica nanoparticles as a function of chain length, core size, and approach velocity. We report results for explicit-atom models of poly(ethylene oxide)-coated nanoparticles in water and alkylsilane-coated nanoparticles in decane.

1Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract No. DE-AC04-94AL85000.

12:51PM J21.00007 Photo-fragmentation of the closo-carboranes , JING LIU, DANQIN FENG, P.A. DOWBEN, Dept. of Physics and Astronomy, University of Nebraska-Lincoln, A.P. HITCHCOCK, Dept. of Chemistry, McMaster University, Canada, A.L.D. KILCOYNE, T. TYLISZCZAK, Advanced Light Source, Lawrence-Berkeley Laboratory, J.D. BOZEK, Stanford Synchrotron Radiation Laboratory, E. RUHL,¨ Institut für Physikalische Chemie, Freie UniversitätBerlin, Germany — Single and multi-cation ionic fragmentation of three isomeric carborane cage compounds [closo- 1,2-orthocarborane, closo-1,7-metacarborane, closo-1,12-paracarborane (C2B10H12)] following B 1s and C 1s excitation were studied by time of flight mass + + analysis. The energetic cycles were constructed to gain some insights into some of decomposition processes. CH or BH2 fragment dominates the single ion fragmentation of the closo-carboranes. Double ion fragmentation yields and charge separation mass spectra of all three isomers are generally quite similar in that + + + + + + + + H and BH2 /CH ion pairs, BH2 /CH and Y11ion pairs (where Y = (BH) or (CH)), Y3 and Y9 ion pairs (where Y = (BH) or (CH)) yields dominate. The + + + + + H and BH2 /CH ion pairs dominate at the B 1s threshold for ortho- and metacarborane, while Y1 and Y11ion pairs (where Y = (BH) or (CH)) dominates the multi-photofragment ion yield of paracarborane at the B1s threshold.

1:03PM J21.00008 Coupled quantum dot / quantum shell systems: optical gain, ultrafast charge transport, and single particle blinking. , PATANJALI KAMBHAMPATI, D.M. SAGAR, EVA DIAS, SAMUEL SEWALL, RYAN COONEY, McGill University, AMY GRIMES, DOUGLAS ENGLISH, University of Maryland — The CdSe/ZnS/CdSe core/barrier/shell nanostructure forms an electronically coupled quantum system that is a spherical analog to the quantum well superlattice. The core’s brightness is enhanced via light harvesting by the shell. This material oﬀers an opportunity to study charge transport in spherical nanoscale materials. Here, we present new results on the femtosecond dynamics of radial charge transport in these materials. With a combination of excitonic state selectivity and femtosecond time resolution, we monitor the ultrafast relaxation dynamics of either the core or the shell, having optically excited either phase. The femtosecond experiments reveal strong optical gain as well as evidence of spatially separated biexcitons, and coupling between phases. Finally, we present single dot data on the two-color blinking kinetics of these coupled quantum dot quantum shell systems.

1:15PM J21.00009 Sampling of stable and metastable cluster structures by a first-principles Monte Carlo approach , RALF GEHRKE, KARSTEN REUTER, Fritz-Haber-Institut, Faradayweg 4-6, D-14195 Berlin — Size-selected nano-scale atomic clusters are now systematically becoming accessible in experiment, but characterizing their ground-state and metastable isomer ensemble averages from first principles requires a global and local exploration of vast configuration spaces. We here explore a first-principles Monte Carlo scheme to efficiently sample the minima of the corresponding total energy landscapes. The energetics is obtained at the density-functional theory level, using an all-electron local orbital based first principles code,1 which allows to switch seamlessly from minimal size effective tight-binding like to meV-level chemically accurate basis sets within a single fundamental framework. The sampling strategies rely on basin hopping, using different schemes to create new trial structures. We demonstrate the reliability and performance of the approach for Cu and Si clusters, discussing in particular the scaling behaviour with the system size. 1M. Scheffler and V. Blum; R. Gehrke, F. Hanke, P. Havu, V. Havu, X. Ren, K. Reuter, P. Rinke, A. Sanfilippo, A. Tkatchenko, The FHI - Ab Initio Molecular Simulations (aims) project, www.fhi-berlin.mpg.de/aims 1:27PM J21.00010 The Effects of pH and Acid Type on Porous Alumina Formation , ADAM FRIEDMAN, DERRICK BRITTAIN, LATIKA MENON, Northeastern University Dept. of Physics — Porous aluminum oxide prepared by anodization has an enormous variety of uses in nanomanufacturing, as it can be used as scaffolding to grow nanowires and tubes of exacting size specifications. However, there is no complete physical model for its growth. Three models in particular have been suggested in the past. We experimentally study the stability of porous alumina formation and the effects of changing anodization voltage, acid pH, and acid type. Using this information, we show that the models err in their primary assumptions, we pinpoint the location of these errors, and we suggest a method to correct them.

1:39PM J21.00011 Probing the Coulomb Barrier Towards Ionic Fragmentation , SHAUN ARD, NASRIN MIRSALEH-KOHAN, ROBERT COMPTON, University of Tennessee — Quintessential to understanding the stability of multiply charged anions (MCAs) is the characterization of the so-called “Coulomb Barrier” (CB) toward the loss of an excess electron and/or dissociation into charged fragments. The CB arises due to the superposition of the long-range Coulomb repulsion of the excess electron (or anion), and the short-range attractive polarization binding energy of the anion (or fragment). The CB adds to the stability of MCAs, often rendering thermodynamically unstable species to be metastable toward autodetachment or dissociation. The magnitude and shape of the CB is expected to depend heavily on the decay pathway. Whereas dissociation into charged fragments is often the lowest energy pathway for many MCAs, the vast majority of previous research has focused on electron loss. In this work, collision-induced dissociation (CID) is − employed to study fragmentation of disulfonic dianions of increasing “length”. Energy threshold for the production of SO3 plus its conjugate anion are used to estimate the magnitude of the Coulomb barrier to dissociation. These measured thresholds are compared with ab initio calculations of the dissociation energy. The relationship between these magnitudes and the distance between the excess charges will then be discussed.

1:51PM J21.00012 Vibrational modes in metal core-shell nanoparticles1 , A.S. KIRAKOSYAN, T.V. SHAH- BAZYAN, Jackson State University — We study the spectrum of lowest vibrational modes of bimetallic nanoparticles in dielectric surrounding. For solid spherical particles, the mode’s period and decay time are determined by the ratio of particle radius to longitudinal sound velocities in metal and outside medium, respectively. In contrast, in bimetallic nanoparticles, the dependence of both period and damping time on aspect ratio is highly non-monotonic. In particular, for Au/Ag core-shell nanoparticles, in a wide range of aspect ratios, the fundamental mode period is lower than in both Au and Ag solid particles of the same overall size, while the damping time exhibits a minimum at aspect ratios around 0.5. The unique acoustical signature of complex nanostructures allows unambiguous determination of their composition from ultrafast pump-probe and Raman spectroscopy measurements.

1Supported by NSF and NIH.

Tuesday, March 11, 2008 11:15AM - 1:51PM — Session J26 DCP: Focus Session: Quantum Control I Morial Convention Center 218

11:15AM J26.00001 Quantum Control of Femtochemistry in the Gas Phase, Liquid Phase and on Surfaces , GUSTAV GERBER, Univ. of Wuerzburg, Institute of Physics — By using coherent control techniques we control the behavior of quantum systems on their natural fs-time scale by applying ultrashort coherent light fields in the wavelength range from the IR to the UV. These laser pulses can be variably shaped in space and time using a laser pulse shaper consisting of a liquid-crystal display [1]. Laser-optimized femtochemistry in the gas phase and liquid phase is one field in which this new technique is successfully employed. Automated optimization of branching ratios and total product yields of gas phase photodissociation reactions as well as chemically selective molecular excitation in the liquid phase is performed [2][3]. Structural changes of a molecule in the liquid phase have been controlled by laser-optimized photoisomerization of a cyanine dye molecule [4] and of retinal in bacteriorhodopsin [5]. So far, optimal control techniques have been restricted to gas phase and condensed phase optimization experiments. Recently we have demonstrated femtosecond laser-assisted catalytic reactions on a Pd(100) single crystal surface. By applying a closed-loop optimal control scheme, we manipulate these reactions and selectively optimize the ratio of different bond-forming reaction channels, in contrast to previous quantum control experiments aiming at bond-cleavage. The results represent a first step towards selective photocatalysis of molecules. [1] T. Baumert et al, Appl. Phys. B 65, 779 (1997) [2] A. Assion et al, Science 282, 919(1998); T. Brixner et al, J. Mod. Opt. 50, 539 (2003) [3] T. Brixner et al, Nature, Vol. 414, 57 (2001) and J. Chem. Phys. 118, 3692 (2003) [4] G. Krampert et al, Phys. Rev. Lett. 94, 068305 (2005) [5] G. Vogt et al, Chem. Phys. Lett. 433, 211 (2006) P. Nuernberger et al, Phys. Chem. Chem. Phys. 9, 2470 (2007)

11:51AM J26.00002 Quantum control spectroscopy with multipulses , MARCUS MOTZKUS, Philipps- Universität Marburg — The manipulation of molecular vibrations by laser light has been always considered as a very promising means to control chemical reaction. The coherently controlled time-dependent superposition of vibrational states may represent motion along a reaction coordinate and therefore allows for a high degree of selectivity. Pulse shapes for manipulating vibrations can be predicted to be trains of pulses with temporal spacing between the sub-pulses equal to an integer of the vibrational phase. If the manipulation of molecular vibrations with pulse trains is expected to be one of the important mechanisms on the long standing aim of mode selective chemistry, it is necessary to understand its application limits. In this work, the interaction of pulse trains with matter is discussed under the light of time-resolved nonlinear experiments and density matrix simulations. Emphasis is given to the role of electronic coherence between excited and ground-state, to the excited state population relaxation time and to the electronic resonance. In particular the lifetime of the excited state poses a challenge for the coherent control with multipulses and, thus, for the mode filtering capability in the excited state. This is investigated by applying a shaped femtosecond excitation pulse to different molecules in solution and probing the response by transient absorption, nonlinear Raman and DFWM spectroscopy. Finally, the effect of the phase of sinusoidal modulation on the envelope of the multipulse sequence and its consequences on pump-probe spectroscopy is discussed, particularly near zero delay between pump and probe pulses.

12:27PM J26.00003 Strategies for optimal control in complex systems , ROLAND MITRIC,´ Department of Chemistry, Humboldt-University Berlin, Brook-Taylor-Str. 2, 12489 Berlin, Germany — We present strategies for the optimal control of the ground and excited state dynamics in complex systems, based on the combination of the quantum chemical molecular dynamics “on the fly” with the semiclassical Wigner distribution approach [1]. We first demonstrate our strategy for the optimal control of the ground state dynamics based on the MD “on the fly” with explicit treatment of the interaction with the laser field which is optimized using a genetic algorithm [2]. This approach will be illustrated on two prototype systems representing rigid symmetrical molecules and floppy biomolecules with low frequency modes. Our results show that the ground state isomerization process can be selectively driven by ultrashort laser pulses with different shapes which are characteristic for the prototype systems. Furthermore, for the optimal pump-dump control involving ground and excited electronic states we have developed a new “field induced surface hopping” method in which the nuclear dynamics is treated classically while the laser induced electronic transitions are treated fully quantum mechanically. We illustrate our approach on the optimal control of cis-trans isomerization in prototype Schiff base molecular switches. Our theoretical approach allows us to explore the controllability of dynamics in complex systems and to unravel the mechanisms underlying the control of molecular processes. Furthermore, the outlook for laser selective photochemistry of nanoparticles and nanoparticle-biomolecule hybrid systems will be given. [1] V. Bonaˇcić-Koutecký,R. Mitrić, Chem. Rev. 105, 11 (2005). [2] R. Mitrić,V. Bonaˇcić-Koutecký,Phys. Rev. A, 76, 031405 (2007). 1:03PM J26.00004 Phase control of molecular fragmentation with a pair of femtosecond-laser pulses1 , KARL-MICHAEL WEITZEL, GEORG BREUNIG, GUNTER URBASCH, Philipps Universitaet Marburg — We demonstrate the control of molecular fragmentation on a femtosecond-time scale in two-pulse measurements with a pair of femtosecond-laser pulses. The measurements were performed with o- xylene (C8H10). Parent and fragment-ion yields were recorded as a function of inter-pulse delays, i.e. different relative phases of the excitation pulses. The experiments revealed different fragmentation mechanisms in the temporal region of direct optical overlap and for separated pulses. For overlapping pulses all ion yields followed the excitation intensity which oscillated as a function of inter-pulse delay due to the change of constructive and destructive interference. For + + larger delays, in particular the oscillations of the C and CH3 fragment-ion yield showed a significant deviation from each other. This deviation vanished in measurements with chirped femtosecond-laser pulses where both parent and fragment-ion yields oscillated in phase for all investigated delays. The results are interpreted as a manifestation of optical phase-dependent electronic excitations mapped onto the nuclear fragmentation dynamics.

1work supported by the DFG

1:15PM J26.00005 Coherent control on cold alkali systems , ALBRECHT LINDINGER, FU Berlin — Optimal control of photo-induced molecular processes has attained considerable success in recent years. An important issue in this regard is the information coded in the optimized laser pulse shape which supplies insight about the underlying processes. Small alkali systems are suitable since they exhibit bound states available for resonant transitions with weak fields which aids the theoretical description and thus the interpretation. New control methods are presented to extract the most relevant information from the optimized laser field. Moreover, novel pulse shaper schemes for simultaneous phase, amplitude, and polarization pulse control were designed and applied to alkali dimers, even in a parametric encoding. The results demonstrate the perspectives of adding the polarization and hence all properties of the light field in the pulse modulation. Currently, coherent control was applied to ultracold ensembles motivated by the perspective to perform photoassociation and photostabilization of alkali systems. First results are received regarding optimized multi-photonic excitation to molecular ions and pump-probe experiments exposing signal oscillations. They provide indications for photoassociation and open the perspective for transitions to lower vibrational levels in the electronic ground state, which would be a first step to an internally cold molecular Bose Einstein condensate.

1:27PM J26.00006 Direct frequency comb measurement and control of vibrational dynamics in ultracold molecular samples , AVI PE’ER, JILA, University of Colorado, EVGENY SHAPIRO, MOSHE SHAPIRO, University of British Columbia, Vancouver, JUN YE, JILA, University of Colorado and NIST — We propose a new class of control schemes for robust transfer of population between quantum states via a wave packet that utilize trains of coherent pulses (optical frequency comb). Our approach draws from analogy to adiabatic passage techniques in three-level systems, but is more general. We show that breaking a slow adiabatic passage into a train of short, perturbative pulses, enables highly eﬃcient population transfer between single states through an arbitrary wave packet. Alternatively, it is possible to directly deduce the intermediate multi-state structure by a simple scan of the pulse train parameters (repetition rate and envelope phase), in a method similar to two-dimensional Fourier spectroscopy. Viewed in the spectral domain, these techniques rely on quantum pathway interference in an adiabatic passage. The scheme is most suitable for applications in cold and ultracold molecular samples.

1:39PM J26.00007 Formation of a gas of ultracold LiCs molecules , J. DEIGLMAYR, J. LANGE, S.D. KRAFT, A. GROCHOLA, R. WESTER, M. WEIDEMULLER,¨ Albert-Ludwigs-University Freiburg, Germany, M. AYMAR, O. DULIEU, Laboratoire Aime Cotton, Orsay, France — Ultracold polar molecules offer intriguing perspectives for the study of many-body effects in strongly interacting gases and the manipulation by external fields. A promising approach to the creation of a large ensemble of ultracold polar molecules in the absolute translational and electronic ground state is the direct formation of ultracold molecules through photoassociation of ultracold atoms. We recently observed the spontaneous formation of ultracold LiCs molecules in a double species magneto optical trap. After spontaneous decay into the electronic ground state, the molecules were ionized by one-color two-photon ionization and detected with a high-resolution time-of-flight mass spectrometer [1]. Here we present the active photoassociation of ultracold LiCs molecules and discuss the state distribution of the produced ground state molecules. Precise knowledge of the molecular structure is required to find the most efficient route for the creation of molecules. We present ab-initio calculations of excited molecular states of LiCs including spin-orbit coupling and study the alignment and orientation of bialkali molecules in combinations of static electric fields and strong laser fields. The perspectives for the production of molecules in the absolute ground state are evaluated. [1] S. D. Kraft et al., J. Phys. B 39, S993

Tuesday, March 11, 2008 2:30PM - 4:30PM — Session L21 DCP: Focus Session: Clusters, Cluster Assemblies, Nanoscale Materials V Morial Convention Center 213

2:30PM L21.00001 Ab Initio Simulations of Nano-Diamond Surface Reconstruction , WILLIAM MATTSON, RADHAKRISHNAN BALU, US Army Research Laboratory — We have simulated with in the Density Functional Theory (DFT) spherically cut nano-diamonds from bulk diamond at ambient conditions. The 2.6 nanometer diameter sphere is then allowed to relax at 250K and surface reconstruction is observed. Four hemispherical fullerene like regions form on the surface and while the interior maintains the diamond structure, it undergoes compression equivalent to over 30GPa in the bulk. Results of dynamic shearing will be presented.

1 2:42PM L21.00002 TiO2 nanostructures prepared by ferrocene/cobalt catalyst agents , M.E. GOMEZ, J.C. CAICEDO, G. ZAMBRANO, Thin Film Group, Department of Physics, Universidad del Valle, A. A. 25360 Cali, Colombia, A-M. LAZAR, D. CHAUMONT, LRRS and FR 2604 Universit´ede Bourgogne 21078 Dijon, France, Y. LACROUTE, M. SACILOTTI, CMN and LPUB. UFR Sc. Techn. FR 2604 Universit´ede Bourgogne, 9 avenue A. Savary, BP 47870, 21078 Dijon Cedex, France — We present the growth and characterization of TiO2 nanocrystals. Nanostructured growth is obtained in a low-pressure CVD system by using an organometallic precursor Ti(OC3H7)4 as both the Ti and O source catalyzed by both ferrocene (an organometallic precursor) and cobalt metallic clusters prepared by the microwave-assisted polyol method. Two kinds of TiO2 structures were obtained in the cobalt clusters: a) pine-tree like (with short-leaf structure) and b) long-leaf structures as large as a few micrometers in size and both under 10-nm in thickness. Long-leaf TiO2 structures were grown at cobalt grain boundaries. For the growth conditions utilized, the TiO2 structures are composed of both anatase and rutile crystallographic phases.

1This work was accomplished under contract project title FILIMON35 n ANR-05-NANO-016-03 France, and the Excellence Center for Novel Materials - CENM contract 043-2005 with COLCIENCIAS, Colombia. 2:54PM L21.00003 Metal cluster anions produced by attachment of slow electrons: Evapora- tive cooling, cluster energetics, and restructuring of the abundance spectra1 , VITALY KRESIN, ROMAN RABINOVITCH, CHUNLEI XIA, University of Southern California — Metal clusters are able to attach low-energy electrons with very large cross sections by capturing them in a strong long-range polarization potential. But little information has been available about the last stage of the collision process: what happens to the energy deposited by the captured electron, and are the cluster size distributions modified? We have carried out measurements of the mass spectra of negative sodium cluster ions born in the electron-cluster interaction region. Importantly, the arrangement allowed us to monitor the parent and the daughter cluster beams simultaneously. It is found that the electron affinity energy is quickly thermalized and is sufficient to cause rapid evaporative cooling. As a result, - the magic numbers shift from Nan to Nan-1, and a host of other significant changes in the abundance structure are observed, compared to the parent cluster beam. These are well reproduced by a detailed analysis based on the evaporation cascade model, and yield new information about cluster binding energies.

1Supported by NSF

3:06PM L21.00004 Anion Photoelectron Spectroscopy and Density Functional Investigation of Diniobium-Carbon Clusters1 , P.A. CLAYBORNE, Virginia Commonwealth University, K.L. KNAPPENBERGER, JR., University of California, Berkeley and Lawrence Berkely National Laboratory, J.U. REVELES, Virgina Commonwealth University, M.A. SOBHY, C.E. JONES, JR., U.U. GUPTA, I. IORDANOV, J. SOFO, A.W. CASTLEMAN, JR., Pennsylvania State University, S.N. KHANNA, Virginia Commonwealth University — Experimental photoelectron and computational results show diniobium-carbon (Nb2Cn) clusters to coexist in multiple structural isomers: three-dimensional geometries, planar rings and linear chains. Three-dimensional clusters having up to ﬁve carbons are formed preferentially with Nb-Nb bonding, whereas only Nb-C bonding is observed experimentally at six carbons. Clusters consisting of an odd number of atoms are also observed with linear geometries. The larger binary clusters (n ≥ 7) display properties similar to pure carbon clusters. We provide evidence for niobium substitution of carbon atoms.

1The authors gratefully acknowledge support from the US Air Force Oﬃce of Scientiﬁc Research, Grant FA9550-04-1-0066 and FA9550-05-1-0186 and from the Departement of the Army through MURI Grant # W911NF-O6-1-0280.

3:18PM L21.00005 Towards Artificial Molecules: Metallodielectric Clusters , DINA ARONZON, VINOTHAN MANOHARAN, JONATHAN FAN, Harvard University, SEAS — Recent advances in the synthesis of metallic colloids have allowed for an ex- plosion in research into their optical properties. It is now possible to synthesize solid metallic colloids, core-shell colloids that mix different metals, and core shell colloids of metallodielectrics. In this talk I propose a mechanism for further exploring the optical properties of such materials by producing clusters of metallodielectric colloids and studying the relationship between the structure and composition of a colloidal cluster and its optical response. To this end, we synthesized a number of solutions, each of clusters consisting of a different average number of colloids. By doing this, we hope to study the effects of different dielectrics and near neighbor interactions on the plasmonic resonances of the metallic shells in the colloid. In the future, we hope to produce and study high yield, pure samples, both in solution and as photonic crystals. All of these options provide new ways of producing specific optical resonances that can be used in sensors, spectroscopy, optical triggers, and many other applications.

3:30PM L21.00006 Quantum transport in molecular electronic devices described with complex source and sink potentials1 , FRANCOIS GOYER, ALI GOKER, MATTHIAS ERNZERHOF, Universite de Montreal, UNIVERSITE DE MONTREAL TEAM — We present a non-Hermitian model Hamiltonian containing complex potentials [1,2] that is devised to study ballistic transport in molecular electronic devices (MEDs). The complex potentials replace semi-inﬁnite contacts and act as source and sink of probability current density. This approach is rigorous in the sense that the exact wave function is recovered in the interior of the MED. We employ this technique to calculate the conductance through certain prototypical MEDs [3]. We also extend this method [4] such that we can go beyond the one- electron picture by constructing two-electron states explicitly. We present results for simple model system described by Hubbard-type Hamiltonians. The impact of electron correlation eﬀects on the molecular conductance is discussed. [1] F. Goyer, M. Ernzerhof, M. Zhuang, JCP, 126, 144104 (2007). [2] M. Ernzerhof, JCP, to appear nov. 2007. [3] M. Ernzerhof, H. Bahmann, F. Goyer, M. Zhuang, P. Rocheleau, J. Chem. Theory Comput., 2, 1291 (2006); M. Ernzerhof, M. Zhuang, P. Rocheleau, JCP, 123, 134704 (2005). [4] A. Goker, F. Goyer, M. Ernzerhof, work in pogress.

1We gratefully acknowledge support from NSERC

3:42PM L21.00007 Charge carrier solvation on a polymer chain revealed in ab initio computations1 , MICHAEL MAYO, YURI GARTSTEIN, The University of Texas at Dallas, Richardson, Texas, USA — When an excess charge carrier (electron or hole) is added to a semiconducting polymer chain in vacuum, it is well known that the carrier may self-trap into a polaronic state accompanied by a self-consistent localized bond alternation pattern. A different mechanism of self-localization is a solvation of the charge carrier expected to take place when the polymer chain is immersed in a polar medium (such as a common solvents) - in this case a self-consistent pattern of the orientational polarization is formed around a localized charge. The goal of our study is to identify this solvation effect within ab initio computations. Using long carbon atom chains (both hydrogen terminated and rings) as model systems, we employ the hybrid B3LYP density functional within the DFT and the Polarizable Continuum Model to find the resulting electronic level structure and atomic charge densities. Our results clearly show trends towards excess charge self-localization due to the solvation. We suggest that this effect may be of importance for various semiconductor nanostructures in polar environments.

1Collaborative U. T. Dallas-SPRING Research and Nanotechnology Transfer Program.

3:54PM L21.00008 Nanotubes in polar environments: Solvated charge carriers and their dynamics , GEOFFREY USSERY, YURI GARTSTEIN, Dept. of Physics, Univ. of Texas at Dallas, Richardson, TX, USA — Excess charge carriers on semiconducting nanotubes immersed in sluggish polar environments (such as common solvents) can undergo self-localization into polaronic states whose properties are profoundly different from the free band states. We explore such solvated states within the adiabatic continuum framework using a simplified picture of an electron or a hole confined to a cylindrical surface in the 3D polar medium. At the static level, the binding energy of a polaron is evaluated and found to be a sizable fraction (∼ 0.3) of the corresponding Wannier- Mott exciton binding energy, which is expected to substantially decrease the thermal activation energy for the exciton dissociation. We discuss the diffusion and mobility of polarons caused by the dielectric fluctuations of the medium and applied electric fields, as well as the local dielectric relaxation modes in the vicinity of the polaron. We also discuss the electronic (optical) transitions between the localized electronic states within a self-consistent potential well due to the orientational polarization pattern. [1] Yu.N. Gartstein, Phys. Lett. A 349, 377 (2006). [2] Yu.N. Gartstein, T.D. Bustamante, S. Ortega Castillo, J. Phys.: Cond. Matter 17, 156210 (2007). 4:06PM L21.00009 Fluorescent silver atom clusters in DNA hairpin loops1 , PATRICK O’NEILL, ELISABETH GWINN, DIRK BOUWMEESTER, DEBORAH FYGENSON, University of California Santa Barbara — We synthesize fluorescent clusters of silver atoms on DNA hairpins, and systematically vary the loop region to probe the effects of DNA sequence and structure on the optical properties and chemical stability of the Ag clusters. We find that these novel fluorophores only form on the single stranded hairpin loop, have Stoke’s shifts ranging from 60nm to 120nm and can be tuned to emit at wavelengths ranging from 525nm to 670nm. Furthermore, certain DNA geometries support strong excitation of visible fluorescence by 260-280nm light.

1This work was supported by NSF grant CCF-0622257, an NSF GAANN Fellowship, and a UCSB Academic Senate Seed Grant.

4:18PM L21.00010 H2O Nucleation Around Noble Metal Cations , PATRIZIA CALAMINICI, PAVEL OROPEZA ALFARO, MARTIN JUAREZ FLORES, ANDREAS KOSTER,¨ CINVESTAV, Departamento de Quimica, MARCELA BELTRAN, UNAM, J. ULISES REVELES, SHIV N. KHANNA, VCU, Physics Department, CINVESTAV COLLABORATION, UNAM COLLABORATION, VCU COLLABORATION — First principle electronic structure calculations have been carried out to investigate the ground state geometry, electronic structure and binding energy of noble metal cations + (H2O)n clusters containing up to 10 H2O molecules. The calculations are performed with the density functional theory code deMon2k [1]. Due to the very ﬂat potential energy surface of these systems special care to the numerical stability of energy and gradient calculation must be taken.Comparison of the results obtained with Cu+, Ag+ and Au+ will be shown. This investigation provides insight into the structural arrangement of the water molecules around these metals and a microscopic understanding of the observed incremental binding energy in the case of the gold cation based on collision induced dissociation experiments. [1] A.M. K¨oster,P. Calaminici, M.E. Casida, R. Flores-Moreno, G. Geudtner, A. Goursot, T. Heine, A. Ipatov, F. Janetzko, J. Martin del Campo, S. Patchkovski, J.U. Reveles, A. Vela and D.R. Salahub, deMon2k, The deMon Developers, Cinvestav, 2006

Tuesday, March 11, 2008 2:30PM - 5:18PM — Session L26 DCP: Focus Session: Quantum Control II Morial Convention Center 218

2:30PM L26.00001 Hiking Over Quantum Control Landscapes , HERSCHEL RABITZ, Princeton University — Seeking the best control over a posed quantum dynamic objective entails climbing over the associated control landscape, which is defined as the quantum mechanical observable as a function of the controls. The topology and general structure of quantum control landscapes as input output maps dictate the final attainable yield, the efficiency of the search for an effective control, the possible existence of multiple dynamically equivalent controls, and the robustness of any viable control solution. Normal optimization problems in virtually any area of engineering and science typically have landscape topologies that remain a mystery. Quantum mechanics appears out to be quite special in that the topology of quantum control landscapes can be established generically based on minimal physical assumptions. Various features of these landscapes will be discussed and illustrated for circumstances where the controls are either an external field or the time independent portions of the Hamiltonian; the latter circumstance corresponds to subjecting the material or molecules to systematic variation and hence viewed in the context of being controls. Both theoretical and experimental findings on control landscapes and their consequences will be discussed, including issues of robustness to noise, search algorithm efficiency, existence of multiple control solutions, prospects for identifying reduced sets of control variables, simultaneous control of multiple quantum systems (optimal dynamic discrimination (ODD)), and mechanism analysis.

3:06PM L26.00002 Non-resonant, non-perturbative Dynamic Stark Control of Quantum Dy- namics. , ALBERT STOLOW, National Research Council — One of the most important non-resonant interactions is the dynamic Stark effect. In the non-perturbative but non-ionizing limit, an effective Hamiltonian can be constructed based upon a hierarchy of approximations (the Born-Oppenheimer Approx- imation, Slowly Varying Envelope Approximation, the Rotating Wave Approximation). In this situation, the effective Hamiltonian contains first order (dipole) and second order (polarizability) matter-field interactions which can lead to significant yet reversible changes to the molecular Hamiltonian. The first order term leads to a fast evolution which follows each optical cycle. The second order term causes an evolution which follows, by contrast, the envelope of the laser pulse. We discuss the use of the non-resonant second order Dynamic Stark Effect as a tool for controlling quantum systems without any net absorption of light. We illustrate this by examples chosen from problems in: (i) Control of branching ratios during non-adiabatic photodissociation; (ii) Control of 3D field free molecular frame alignment of asymmetric tops.

3:42PM L26.00003 Controlling and Understanding Laser Filamentation in the Solution and Gas Phase Molecular Systems , ROBERT J. LEVIS, Temple University — The process of laser filamentation is highly nonlinear, yet amenable to control using laser pulse shaping techniques. Investigations of our ability to control the spatial position of a filament in a water tank and measurements of the forward and back scattered amplified spontaneous emission (resulting from the strong field excitation in the resulting plasma) will be presented. Our time resolved measurements of the dynamics of the filamentation process in various gases will also be reviewed. Finally, a model of the plasma formation will be presented.

4:18PM L26.00004 New Developments in Quantum Control: Phase Space Learning Algorithms and Uncontrollable Quantum Systems1 , DAVID J. TANNOR, Department of Chemical Physics, Weizmann Institute of Science — This talk has two parts. The first deals with a new representation of shaped ultrafast laser pulses based on a von Neumann time-frequency√ lattice. We show that√ a pulse defined in terms of an amplitude and a phase at N frequency points can be represented on the von Neumann lattice using N points in frequency and N in time without loss of information. The transformation from the frequency (or time) representation to the von Neumann representation is one-to-one and therefore invertible. We discuss three possible applications of the von Neumann representation of pulses: 1) for cleaning and interpreting complex pulses; 2) for performing systematic scans of the effect of timing and frequency on molecular control; 3) as genes to be used in mutations and crossover in evolutionary algorithms. The second part of the talk deals with the classification of uncontrollable quantum systems. It is well-known that for a quantum system to be controllable the Lie algebra spanned by iterated commutators of H0 and H1 must span the full space of the dynamical algebra. We pose the following questions: When a system is not completely controllable, can we classify different families of uncontrollable systems? If so, can we associate these different types of mathematical structures with different underlying physics (for example, dark states or generalized entangled states)? We show that uncontrollable quantum systems fall into two categories: reducible and irreducible. The former is associated with dark states and the latter with generalized entangled states. Based on Lie subalgebras we give a complete characterization of irreducible uncontrollable systems for systems up to 9 levels. Finally, we show that an earlier intuitive concept of connectivity only incompletely captures this Lie algebraic structure of uncontrollable systems.

1The first part of this work was done in collaboration with Susanne Fechner, Frank Dimler, Tobias Brixner, and Gustav Gerber, University of Wuerzburg. The second part was done in collaboration with Thomas Polack and Haim Suchowski, Weizmann Institute. 4:54PM L26.00005 Quantum information processing with a minimal control , PETER PEMBERTON- ROSS, SONIA SCHIRMER, DAMTP, University of Cambridge, IVAN PULLEN — Various physical and practical constraints limit the amount and type of control we have in quantum information processing systems, leading to complicated or unreliable implementations. To try and circumvent these problems, we take the most restricted candidate systems where only a single energy transition can be controlled by a piecewise-constant field, and show that even this is sufficient for efficient execution of a range of useful QIP tasks. We show that it is in principle possible to achieve global control with a single, simple, fixed, local actuator, and show how such minimal control could significantly improve information processing in terms of speed, fidelity and transfer efficiency. The scheme presented has a natural application to spin-chain systems, where only one interaction between two spins can be controlled, and the effects of the position of the controller in the ’quantum wire’ and the system’s symmetries are explored. It may also be relevant for gate-controlled solid-state systems where it is desirable or necessary to limit the number of control electrodes due to the constraints of size, decoherence and cross-talk, and where complex temporal variation of the control voltages is difficult.

5:06PM L26.00006 A Simulation of Strong-Field Attosecond Electron Dynamics: Effects of Pulse Shape , STANLEY SMITH, DMITRI ROMANOV, Temple University, XIAOSONG LI, University of Washington, H. BERNHARD SCHLEGEL, Wayne State University, ROBERT LEVIS, Temple University — As the complexity of systems increases from atoms to molecules, the exploration of nonadiabatic electron dynamics in strong fields requires a leap in understanding and in the principles of description. Recently, a time-dependent Hartree-Fock approach (TDHF) was developed to study the dynamics of individual electrons in multielectron systems. We have used this TDHF approach to numerically simulate the non-adiabatic electron dynamics of a few small molecules and polyacenes using basis sets ranging from AUG-cc-pVTZ for smaller molecules to 6-31G(d,p) for larger molecules. The electric field was applied in the direction of the long molecular axis and the attosecond response of the electrons during and after the laser pulse has been obtained. To determine the effects of ionization, electron dynamics for both neutrals and ions was also simulated. As a function of pulse shape, there are significant differences in the excitation spectrum and volume for each molecule.

Wednesday, March 12, 2008 8:00AM - 11:00AM — Session P21 DCP: Focus Session: Fundamental Issues in Catalysis I Morial Convention Center 213

8:00AM P21.00001 The role of hot electrons in catalysis science , GABOR A. SOMORJAI, Department of Chemistry, University of California Berkeley — One long-standing observation in the field of heterogeneous catalysis is that the activity and selectivity in certain reactions is dramatically affected by the oxide onto which the metal nanoparticles are deposited, even though the oxide itself is not active in catalysis. Recently, studies which detected hot electron formation at metal surfaces helped to explain these curious findings. Pulse probe experiments have detected hot electron formation within femtoseconds when photons are incident on a metal surface. Experiments indicate that the mean free path of these hot electrons is on the order of 5 nm, which is in the range of the size of catalyst nanoparticles. Further studies indicate that exothermic catalytic reactions can also produce hot electrons readily, for example CO oxidation or the reaction of hydrogen and oxygen to form water. We have constructed a “catalytic nanodiode” in our laboratory whereby we carry out catalytic reactions at high and continuous turnover and, using a Schottky barrier, collect hot electrons. Simultaneous measurement of turnover frequency and hot electron current during CO oxidation has shown that the hot electron current and the turnover rate for the reaction are correlated. This implies that the catalytic activity at the oxide-metal interface in certain catalytic reactions is associated with the hot electron flow.

8:36AM P21.00002 CO oxidation over noble metals: The continuum from ultrahigh vaccuum to atmospheric pressures , DAVID GOODMAN, Texas A&M University — Catalytic oxidation of CO has been investigated for many decades by numerous researchers and is considered to be one of the best understood catalytic reactions. Because of its importance in pollution control, fuel cells, etc., this reaction has received considerable attention for fundamental and practical reasons. Removal of CO from automobile exhaust is accomplished by catalytic converters using supported Pt-group metals of Pt, Pd and Rh catalysts. The catalytically removal of traces of CO from H2 by Pt-group metals to the few ppm level is required for efficient operation in fuel cells. Efforts in our laboratory have addressed the adsorption of CO and the kinetics of CO-oxidation on single crystals and supported metal catalysts over a wide temperature (400–650 K) and pressure (1×10−7 ∼500 Torr) range. Two active phases, CO-dominated and O-dominated, have been identified for which the mechanisms for CO catalytic oxidation are entirely different. The highly active phase formed in oxygen-rich reaction condition exhibits CO2 formation rates several orders higher than the rates found for stoichiometric reaction conditions. This highly active surface was determined to consist of approximate one monolayer of surface oxygen using Auger spectroscopy and X-ray photoemission spectroscopy.

9:12AM P21.00003 Gold atoms, chains and islands on oxide ﬁlms: looking at orbitals and counting electrons. , HAJO FREUND, Fritz Haber Institute of the Max Planck Society — Low-temperature STM measurements combined with DFT calculations are employed to analyze the adsorption of gold on alumina/NiAl(110). The binding of Au monomers involves breaking of an oxide Al-O bond below the adatom and stabilizing the hence under-coordinated O ion by forming a new bond to an Al atom in the NiAl. The adsorption implies negative charging of the adatom. The linear arrangement of favorable binding sites induces the self-organization of Au atoms into chains. For every ad-chain, the number of electrons, in particular of transfer-electrons from the support, is determined by analyzing the node structure of its HOMO.

9:48AM P21.00004 Theoretical Insights into C1 Surface Chemistry , MATTHEW NEUROCK, University of Virginia — Reforming and partial oxidation of methane as well as other C1 fuels are important processes in the production of hydrogen and synthesis gas and will likely play important roles future energy strategies. Herein we use theory and simulation to examine the reactivity of methane, methanol and dimethyl ether with CO2,H2O, or O2 over supported transition metals. We systematically probe the elementary C-H bond activation as well as the oxidation pathways involved in both reforming as the oxidation of methane and other C1 intermediates over well deﬁned transition metal surfaces, metal alloys and metal nanoparticles. The calculations demonstrate well-established trends in C-H bond activation as the result of changes in the metal, the activating molecule (methane, methanol, and DME) as well as the reaction conditions. The reaction conditions ultimately dictate the surface coverage of carbon and oxygen which have important consequences on the surface reactivity. The theoretical and simulation results are compared with well deﬁned experiments carried out at Berkeley over supported particles.

10:24AM P21.00005 Atomic ordering periodicity and catalytic properties of nanoparticles , VALERI PETKOV, Central Michigan University — Often nanosized particles of crystals are catalytically very active while the corresponding crystals are not. A typical example is gold. The enhanced catalytic performance of nanosized particles, however, does not come merely from their greatly enhanced surface- to-volume ratio. We would like to draw attention to the often overlooked fact that nanosized particles of crystals do not necessarily possess the periodic 3D structure of their bulk counterparts, and this too may impact their catalytic properties substantially. In particular, nanoparticles that do not have a periodic 3D structure may not come in a well-defined, faceted shape, i.e. may not be terminated by well-defined (usually high energy) atomic planes, as crystalline objects of the same size would be. Hence, nanoparticles may be catalytically more (or less) active than “nanosized” crystals. Results from recent structure studies (synchrotron XRD and computer simulations) on 1 – 5 nm Ru, Au and Pt particles will be presented as evidence. 10:36AM P21.00006 First-principles investigation of Ag-Cu alloy surfaces in an oxidizing environment , SIMONE PICCININ, CATHERINE STAMPFL, The School of Physics, The University of Sydney, Australia, MATTHIAS SCHEFFLER, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Germany — By means of density-functional theory, together with concepts from atomistic thermodynamics, we present a theoretical procedure for describing the structure and stoichiometry of a binary alloy in contact with a surrounding gas phase environment. We apply the approach to the Ag-Cu alloy in an oxygen atmosphere, for which recent results report a superior selectivity for ethylene epoxidation compared to pure silver, the predominant catalyst for this reaction. We first show that the presence of oxygen leads to copper segregation to the surface. Then, considering the surface free energy as a function of the surface Cu composition, we construct the “convex hull”. By including the dependence of the surface free energy of the oxygen chemical potential, we determine the phase diagram of the alloy as a function of temperature, pressure, and Cu surface content. We predict that for conditions typical of the epoxidation reaction, a number of structures can be present on the surface of the alloy including the clean silver surface, thin copper-oxide-like structures, and thick copper oxides. These findings are consistent with, and help explain the recent experimental results. We envisage this approach will be useful and generally applicable for the study of other alloys in contact with a gas or liquid phase.

10:48AM P21.00007 The Cu/ZnO(0001) Surface under Oxidative and Reducing Conditions: A First-principles Study , KATAWUT CHUASIRIPATTANA, OLIVER WARSCHKOW, University of Sydney, School of Physics, BERNARD DELLEY, Paul Scherrer Institut, Villigen Switzerland, CATHERINE STAMPFL, University of Sydney, School of Physics — The Cu/ZnO(0001) surface is widely used as a catalyst for the production of H2-gas from methanol and is thus of considerable relevance to the emergent hydrogen economy. A key to the further development of this catalyst system is a detailed atomic-scale understanding of the relation between surface structure and function versus environmental conditions such as copper content and state of surface oxidation. Towards this goal, we use density functional theory within the framework of ab initio atomistic thermodynamics to conduct a detailed survey of conceivable surface structures under variety of Cu exposures. This produces a surface phase diagram that reveals several distinct regimes of surface reconstruction under oxygen-rich and poor conditions. We correlate our ﬁndings with experimental studies, including recent scanning tunneling microscopy results by Dulub et al [1]. References: [1] O. Dulub, M. Batzill, and U. Diebold, Topics in Catalysis 36 (2005) 65.

Wednesday, March 12, 2008 8:00AM - 10:48AM — Session P26 DCP: Focus Session: Quantum Control III Morial Convention Center 218

8:00AM P26.00001 Use of Ultrafast Molecular Dynamics and Optimal Control for Identifying Biomolecules , JEAN-PIERRE WOLF, University of Geneva — With F.COURVOISIER,L.GUYON,V.BOUTOU, and M.ROTH,J. ROSLUND, H. RAB- ITZ, Princeton University. The identification and discrimination of molecules that exhibit almost identical structures and spectra using fluorescence spectroscopy is considered quite difficult. In order to evaluate the capability of optimal control for discriminating between the optical emissions of nearly identical molecules, we developed a new approach called “optimal dynamic discrimination (ODD). A proof of principle ODD experiment has been performed using Riboflavin (RBF) and Flavin Mononucleotide (FMN) as model system. We used a complex multipulse control field made of a pair of pulses (UV and IR). The UV part (400 nm) is optimally shaped using a control learning loop while the IR component (800 nm) is FT-limited (100 fs) and set at a definite time delay with respect to the UV pulse. Clear discrimination was observed for optimally shaped pulses, although the linear spectra from both molecules are virtually identical. A further experiment showed that, by using the optimal pulse shapes that maximize the fluorescence depletion in FMN and RBF in a differential manner, the concentration of both molecules could be retrieved while they were mixed in the same solution. The ODD demonstration sets out a promising path for future applications, as for example fluorescence microscopy where endogenous fluorescence spectra of many biomolecules overlap.

8:36AM P26.00002 Spinning Tops in External Fields. From High Harmonic Generation to Control of Transport in the Nanoscale1 , TAMAR SEIDEMAN, Northwestern University — Nonadiabatic alignment is a coherent approach to control over the spatial properties of molecules, wherein a short, moderately- intense laser pulse is applied to populate a broad rotational wavepacket with fascinating properties. In the limit of small isolated molecules, nonadiabatic alignment has evolved in recent years into an active ﬁeld of theoretical and experimental research with a rich variety of applications. Following a brief review of the essential physics underlying nonadiabatic alignment, we discuss one of these applications, namely the use of high harmonics generated from aligned molecules as a probe of the underlying electronic dynamics and rotational coherences. Next, we extend the alignment concept to dissipative media, including dense gases, solutions, and interfaces. We illustrate the application of rotational wavepackets as a probe of the dissipative properties of dense media and propose a means of disentangling population relaxation from decoherence eﬀects via strong laser alignment. We extend alignment to control the torsional motions of polyatomic molecules, and apply torsional control in solutions to manipulate charge transfer events, suggesting a potential route to light controlled molecular switches. Turning to interfaces, we introduce a route to guided molecular assembly, wherein laser alignment is extended to induce long-range orientational order in molecular layers. Finally, we combine the nonadiabatic alignment concept with recent research on nanoplasmonics and on conductance via molecular junctions to develop an approach to optical control of transport in the nanoscale.

1We are grateful to to the US Department of Energy (Grant No. DE-FG02-04ER15612) for support.

9:12AM P26.00003 Enhancing vibrational selectivity and 2D IR spectroscopies with mid-IR pulse shaping , MARTIN ZANNI, University of Wisconsin — We report on the capabilities of a new pulse shaper that operates directly in the mid- infrared. This shaper can adjust the phase and amplitudes of 500 frequency elements to generate complex time-domain pulses. In this talk, experiments will be reported using this shaper to coherently control the vibrational excitations of condensed phase molecules with adaptive learning feedback control. We will also report how this shaper can be used to collect two-dimensional infrared (2D IR) spectra by programming the pulse sequences. 2D IR spectroscopy via pulse shaping is extremely rapid, highly accurate, and more ﬂexible than traditional means for collecting spectra. Taken together, mid-IR pulse shaping allows for new experiments in ground state coherent control and probing vibrations with unprecedented accuracy using new multidimensional spectroscopies.

9:48AM P26.00004 Combined Dimensionality Reduction in Search and Detection Spaces via Diffusion Mapping , DMITRI ROMANOV, Dept. of Physics and Center for Advanced Photonics Research, Temple University, Philadelphia, PA 19122, STANLEY SMITH, JOHN BRADY, Dept. of Chemistry and Center for Advanced Photonics Research, Temple University, Philadelphia, PA 19122, RONALD COIFMAN, Dept. of Applied Mathematics, Yale University, New Haven, CT 06511, ROBERT LEVIS, Dept. of Chemistry and Center for Advanced Photonics Research, Temple University, Philadelphia, PA 19122 — Strong-field control settings involve highly nonlinear processes. Typically, both search and detection spaces are high-dimensional (with dimension ∼100 each). This poses considerable problems to analysis and interpretation of the process-related data. Here, we use the recently developed nonlinear statistical method of diffusion mapping to effectively reduce the combined dimensionality of the search and detection space and to sample essential patterns in the lower-dimensional representation. The diffusion maps are constructed and analyzed for the case study of maximizing integrated intensity in a second harmonic generation experiment. The use of a sampling set of 1000 random pulses in the diffusion mapping is sufficient for effective dimensionality reduction and for revealing the inherent structure of the process-related data. Extrapolation of the low-dimensional diffusion-space pattern helps indicate the area in the search space that is most amenable to effective optimization. The diffusion-mapping algorithm is sufficiently fast and robust that may make it a valuable preprocessing tool for optimal pulse searching. 10:00AM P26.00005 Selective Rotational Manipulations of Close Molecular Species – isotopes and isomers , YEHIAM PRIOR, SHARLY FLEISCHER, ILYA SH. AVERBUKH, Department of Chemical Physics, Weizmann Institute of Science, Rehovot, Israel 76100 — We experimentally demonstrate a new approach to selective excitation of close molecular species in mixtures. We apply two time delayed, ultrashort laser pulses where the first pulse rotationally excites both components in a binary mixture, and the second pulse de-excites one, while enhancing the excitation degree of the other. In our work we implemented this approach to molecular nitrogen, and study the cases of molecular isotopes and molecular spin isomers. The case of molecular isotopes is based on the mass difference between the molecular components which results in a slightly different revival period of the repetitive alignment that follows excitation by an ultrashort pulse. Following the revival process, one can distinguish between the isotopic components and selectively affect them. The case of spin isomers is more complicated since there are no differences in their mechanical or electrical properties. Here we utilize the symmetry and statistics of the specific molecular wavefunction and demonstrate highly selective (∼18:1) excitation of Ortho/Para nitrogen. Numerical simulations agree very well with the observed results. Since this process is nonresonant and does not require any special conditions like temperature etc. this approach is general and can be applied to most symmetric molecules.

10:12AM P26.00006 Anti-Correlated Pigment Fluctuations of Allophycocyanin for Highly Ef- ficient Photosynthetic Light Harvesting in Cyanobacteria , ANDREW MORAN, University of North Carolina, RENE NOME, NORBERT SCHERER, University of Chicago — The phycobiliprotein, allophycocyanin (APC), is an excellent model system for the study of light harvesting pigment interactions with a protein bath. This work investigates the relaxation of electronic excitations in APC with electric field-resolved transient grating and photon echo spectroscopies. Transient grating experiments observe a 35 fs internal conversion process between single exciton levels. Most importantly, our analysis shows that anti-correlated phycocyanobilin pigment energy level fluctuations cause the anti-diagonal orientation of the node in the measured dispersive photon echo spectrum. We believe this novel observation to reflect concerted protein bath fluctuations over the 2 nm length scale that separates the pigments. Consideration of the Forster energy transfer rate theory suggests that APC has evolved with this property to enhance its photosynthetic light harvesting efficiency.

10:24AM P26.00007 ABSTRACT WITHDRAWN — 10:36AM P26.00008 Understanding the relaxation of excited-state cis-1,3,5-hexatriene in order to augment the preferred pathway for control , MICHAEL OROZCO, KUO-CHUN TANG, ROSEANNE SENSION, Dept. of Chem., University of Michigan- Ann Arbor — A study of the ground and excited-state relaxation of cis-1,3,5-hexatriene in various solvents and temperatures has been performed. The role solvent plays in the relaxation dynamics and relaxation pathways has been assessed and modeled to achieve a better understanding of the energy landscape. This information will be used to determine the preferred relaxation pathways and inform eﬀorts to use sculpted UV pulses to inﬂuence the excited state dynamics through pump-dump interactions. Finally, further experiments are proposed wherein UV pulse-shaping will used to study and control other reactive systems.

Wednesday, March 12, 2008 11:15AM - 2:15PM — Session Q21 DCP: Focus Session: Fundamental Issues in Catalysis II Morial Convention Center 213

11:15AM Q21.00001 ”Heterogeneous Electrocatalysis” , ANDRZEJ WIECKOWSKI, University of Illinois, Champaigne — No abstract available.

11:51AM Q21.00002 Tailoring Surface Reactivity of Metal Oxides , ULRIKE DIEBOLD, Department of Physics, Tulane University, New Orleans, LA 70118 — Titanium oxide is receiving continued attention because of its importance as catalyst support, as a material to harvest solar energy for chemical transformations, and as a model metal oxide. In this talk, I will focus on the structure and defects (extrinsic and intrinsic) of less-studied TiO2 surfaces; i.e., rutile (011)-2x1 and anatase (101), and their inﬂuence on surface reactivity.

12:27PM Q21.00003 ”Understanding Reaction Pathways on Model Catalyst Surfaces” , WILFRED TYSOE, University Wisconsin Milwaukee — No abstract available.

1:03PM Q21.00004 Modulating the reactivity of Pt-based catalysts for PEMFC: A First Prin- ciples Study , HAI-YAN SU, XIN-HE BAO, WEI-XUE LI, Dalian Institute of Chemical Physics, CAS, Dalian, China — Low-temperature Polymer electrolyte membrane fuel cells (PEMFCs) have been regarded as one of the most promising candidates to produce heat and electricity, especially for electric vehicles or residential co-generation systems. However, the CO poison at the anode and the slow kinetics of the ORR at the cathode for Pt based-catalysts limit its widespread application, which motivated extensive research for more effective catalysts with CO tolerant, highly active and lower Pt loading, and/or highly selective for CO PROX. Density functional theory calculations have been used to screen Pt-based catalysts for PEMFC. It is found that the direct contact with Pt catalysts (so-called Pt-skin) is essential. The reactivity of Pt-skin catalysts towards the oxygen reduction reaction (ORR) and the hydrogen evolution reaction (HER) can be modulated by stepwise increase of Ni contents, which are accomplished by the modification of the reactivity through ligand and geometrical effects. The overall reactivity is however balanced by effective adsorption and desorption of adsorbates. Our calculations show that among various PtxNiy with Pt-skin, Pt3Ni is the catalyst with the highest overall reactivity. The present work indicates that it may be a good candidate for CO preferential oxidation (PROX) in excess of the hydrogen.

1 1:15PM Q21.00005 Surface Site Characterization of COads on Platinum , PATRICK MCGRATH, AURORA MARIE FOJAS, ELTON CAIRNS, JEFFREY REIMER, University of California - Berkeley — Nuclear magnetic resonance (NMR) spectroscopy is used in conjunction with cyclic voltammetry (CV) to explore the surface chemistry of CO on platinum electrocatalysts. Electrochemically prepared COads (from different sources and electrode potentials) are studied on platinum at various coverages in sulfuric acid electrolyte. A model is presented to parse the total oxidation current into its separate contributions and these are correlated with the type of surface site occupied by the adsorbate. Accounting of the CV oxidation 13 currents suggest that the species left on the surface after partial oxidation of a saturated COads layer is a mixture of linear- and bridged-CO. C-NMR of the surface species resulting from electrochemically adsorbing labeled methanol provides direct insight into the surface electronic structure of the catalysts. We observe a shift in the 13C-NMR spectra associated with different surface preparations. These shifts correlate with the corresponding coverage of the adsorbate on different types of platinum sites. NMR is used to probe the dynamics of these species to elucidate the interaction of the adsorbate with the platinum surface.

1Based on work supported by the U. S. Army Research Laboratory and the U. S. Army Research Office under contract/grant number 48713CH. 1:27PM Q21.00006 Does Pauli repulsion induce the dissociation energy barriers? A first principles study , MASATO ITO, SHIGEYUKI TAKAGI, HIDEKAZU TOMONO, KAZUO TSUMURAYA, Meiji University, JAPAN — We elucidate the origin of the formation analyzing the dissociation process of oxygen molecule on bridge-top-bridge site of Pt(111). The charge state is analyzed by the Bader method together with the spin states of the two oxygen atoms. The charge transfers to the dissociated oxygen molecule from the Au surface. The potential energy variation is in agreement with the energy variation of the separated in distance, charged, and spin polarized oxygen molecules that is calculated with real- space density functional method. Excluding the exchange term in the total energy calculation of the H2/Au system leads to a monotonic increase of the potential energy surface in the dissociation process. The energy barriers in the H2/Mg, H2/Pt, and H2/Au systems are in agreement with the energy variations of the charged, isolated, and separated hydrogen molecules. The barriers appear in late dissociations although no barrier for the nondissociated adsorptions. Their electronegativity differences determine the directions of the transfer in the cases investigated. So we have to reconsider the applicablity of the Pauli repulsion to the barrier formations.

1 1:39PM Q21.00007 O2 Dissociative Adsorption on Cu2O(100) with O Vacancies , DUY LE, SERGEY STOLBOV, TALAT RAHMAN, University of Central Florida — Cu2O surfaces and nanoparticles have been shown to have high activity for CO oxidation [1]. As a result of consumption of the surface oxygen during the CO oxidation process on Cu2O(100), the issue of restoration of the surface composition becomes critical. Through ﬁrst principles electronic structure calculations of the geometry, activation energy barriers, reaction pathways, and the local densities of electronic states for O2 dissociative adsorption on the Cu2O(100) surface with O vacancies, we show that the healing of oxygen vacancies is accompanied by reconstruction of the surface. Our calculations are based on density functional theory in the generalized gradient approximation and usage of ultrasoft pseudopotential method in the plane wave representation. [1] B. White, M. Yin, A. Hall, D. Le, S. Stolbov, T. S. Rahman, N. Turro, and S. O’Brien, Nano Lett., 6, 2095 (2006).

1Work supported in part by DOE under Grant No. DE-FG02-07ER15842. Computational resources: TeraGrid grant No: DMR050039N.

1:51PM Q21.00008 Modeling the effects of the oxide substrate on O2 dissociative adsorption on Au nanostructures1 , SERGEY STOLBOV, TALAT S. RAHMAN, University of Central Florida — In this work we apply the density functional theory calculations to explore the mechanism of high reactivity of Au nanoparticles on oxide substrates. We test the idea that the substrate – nanoparticle interaction makes the O2 dissociative adsorption favorable on this system, in contrast to bulk Au, and then the O atoms, so adsorbed, are consumed by reactants for further oxidation. We exploit the observation that the 2-layer Au film on TiOx displays an exceptionally high reactivity as compared to a monolayer Au film, as well as those with 3 or more layers [1]. We calculate the energy Eda of dissociative adsorption of O2 on the surfaces 1, 2, 3, and 5 Au(111) layer structures in two environments: 1) free standing layers, 2) on TiO fragments (modeling a substrate). We find Eda to be negative for the 2- and 3-layer Au films on the “substrate” while it is positive for all other systems under consideration. This result along with the experimental finding [1] point to the O2 dissociative adsorption as being the main mechanism for the observed reactivity of Au nanostructures. Calculated local densities of electronic states and local charges in the system will be presented for further insights into the nature of the effect. [1] M. S. Chen, D. W. Goodman, Science 306, 234 (2004).

1Work supported in part by DOE under grant # DE-FG02-03ER15842.

2:03PM Q21.00009 A Density Functional Theory study of Cobalt nanoparticle catalyst for Fischer-Tropsch Synthesis1 , CHANDANA GHOSH, Department of Chemical Engineering, Unviersity of South Florida — In the Fischer- Tropsch synthesis Cobalt nanoparticles are widely used as catalysts in which the reaction of Carbon Monoxide and Hydrogen form hydrocarbons. Particle sizes in the range of 6-8 nm have shown to exhibit maximum catalytic activity which is attributed to their surface area and their ability to stabilize steps. Using ab-initio electronic structure calculations based on the density functional theory we study the energetics of adsorption and dissociation of Carbon Monoxide on various particle morphologies and coverages including flat and stepped surfaces and particles with a separation of a few angstroms. The local density of states will be calculated for the various configurations. This study will provide an in-depth understanding of the energetics of adsorption and dissociation of Carbon Monoxide on Cobalt particles and for the various coverages and the particle configurations that lower the dissociation barrier as well as the preferred adsorption sites of the atoms that give the lowest energy for the various particle geometries.

1NASA

Wednesday, March 12, 2008 11:15AM - 2:15PM — Session Q26 DCP: Advances in Spectroscopy Morial Convention Center 218

11:15AM Q26.00001 IR and Raman spectroscopy of water and ice by ab initio simulations1 , MANU SHARMA, DAVIDE DONADIO, GIULIA GALLI, UC Davis — We use ab initio molecular dynamics to compute the IR and Raman spectra of a variety of heavy water systems, ranging from pure water and ice, to liquid water confined between graphene foils and D-terminated diamond surfaces. The analysis of the simulated spectra provides the fingerprints of different hydrogen bonding environments, giving access to the complex structural and dynamical properties of water in various conditions. In addition our results provide a detailed, microscopic interpretation of IR and Raman experiments, as they allow us to assign univocaly spectroscopic bands to specific vibrational modes, and to identify electro-dynamic coupling between water molecules and surfaces, in the case of confined water. Our MD simulations also give a quantitative estimate of the anharmonicities and lifetimes of various vibrational modes.

1This work was performed under the auspices of the DOE under contract no. W-7405-Eng-48

11:27AM Q26.00002 Infrared spectra of ice and water from first principles: intra vs. intermolecular dipole correlations1 , WEI CHEN, Department of Physics, Princeton University, Princeton, NJ 08544, USA, MANU SHARMA, Department of Chemistry, University of California, Davis, CA 95616, USA, RAFFAELE RESTA, Dipartimento di Fisica Teorica, Universitàdi Trieste, Strada Costiera 11, 34014 Trieste, Italy, GIULIA GALLI, Department of Chemistry, University of California, Davis, CA 95616, USA, ROBERTO CAR, Department of Chemistry, Princeton University, Princeton, NJ 08544, USA — We report simulated infrared (IR) spectra of deuterated ice and water using Car-Parrinello molecular dynamics with maximally localized Wannier functions. Experimental features of both ice and water are accurately reproduced within the harmonic approximation. Calculated line shapes are further decomposed in terms of intra and intermolecular dipole correlation functions with spatial resolution. This approach proves to be very useful to understand the origin of spectral features and the nature of the underlying hydrogen-bond (H-bond) network. We find that intermolecular dynamic charge fluctuations play a crucial role over the entire frequency range.

1This work is partially supported by NSF under the PCCM-MRSEC program with award number: NSF DMR 02-13706. 11:39AM Q26.00003 Nuclear quantum effects in water1 , JOSEPH MORRONE, ROBERTO CAR, Dept. of Chemistry, Princeton University — In this work, a path integral Car-Parrinello molecular dynamics2 simulation of liquid water is performed. It is found that the inclusion of nuclear quantum effects systematically improves the agreement of first-principles simulations of liquid water with experiment. In addition, the proton momentum distribution is computed utilizing a recently developed “open” path integral molecular dynamics methodology3. It is shown that these results, which are consistent with our computations of the liquid structure, are in good agreement with neutron Compton scattering data4. The remaining discrepancies between experiment and the present results are indicative of some degree of over-binding in the hydrogen bond network, likely engendered by the use of semi-local approximations to density functional theory in order to describe the electronic structure.

1This work was supported by the Fannie and John Hertz Foundation and DOE grant DE-FG02-05ER46201 2CPMD V3.11 Copyright IBM Corp 1990-2006, Copyright MPI fuer Festkoerperforschung Stuttgart 1997-2001. 3J.A. Morrone, V. Srinivasan, D. Sebastiani, R. Car J. Chem. Phys. 126 234504 (2007). 4G.F. Reiter, J.C. Li, J. Mayers, T. Abdul-Redah, P. Platzman Braz. J. Phys. 34 142 (2004).

11:51AM Q26.00004 ABSTRACT WITHDRAWN —

12:03PM Q26.00005 Fluorescence correlation spectroscopy with Gaussian-Lorentzian volumes , MICHELE MARROCCO, ENEA — Fluorescence correlation spectroscopy (FCS) is a fundamental technique of fluorescence microscopy used for many applications of chemical physics where molecular diffusion plays primary roles [see, for example, O. Krichevsky and G. Bonnet, Rep. Prog. Phys. 65, 251 (2002)]. The milestone of FCS is called three-dimensional Gaussian (3DG) approximation. According to this assumption, the observation volume is modeled by Gaussian profiles along the main three spatial directions. This simplification is necessary to achieve analytical treatment of FCS measurements. In this work, analytical solutions are shown for another geometry corresponding to the fundamental mode of laser beams, i.e. the Gaussian-Lorentzian distribution, where Gaussian profiles are associated with the two transverse directions while a Lorentzian dependence characterizes the axial direction (coincident with the optical axis of the microscope). Analytical solutions are guaranteed for both one-photon and two-photon excitations of diffusing molecules [one-photon excitation is considered in M. Marrocco, Chem. Phys. Lett. 449, 227 (2007)]. Similarities and differences with respect to the 3DG approximation are discussed.

12:15PM Q26.00006 Studying hydrogen bond by Quantum Monte Carlo: binding energy and dispersion curve of the water dimer , LEONARDO SPANU, SISSA-ISAS Trieste, Italy; Dept. of Chemistry UC Davis, FABIO STERPONE, LUCA FERRARO, Caspur Roma, Italy, SANDRO SORELLA, SISSA-ISAS Trieste, Italy, LEONARDO GUIDONI, Univ. La Sapienza Roma, Italy — We present a variational MonteCarlo (VMC) and lattice regularized diffusion MonteCarlo (LRDMC) study of the binding energy and dispersion curve of the water dimer. One the aim of the present work is to investigate how the bonding of two water molecules, as a prototype of the hydrogen-bonded complexes, could be described by a JAGP wave function, an implementation of the resonating valence bond idea.Using a pseudopotential for the inert core of the Oxygen, with a full optimization of the variational parameters, we obtain at the VMC level a binding energy of -4.5(0.1) Kcal/mol, while LRDMC gives -4.9(0.1)Kcal/mol (exp. 5 Kcal/Mol). The calculated dispersion curve reproduces both at the VMC and LRDMC level the miminum position and the right curvature.The quality of the WF gives us the possibility to dissect the binding energy in different contributions by appropriately switching off determinantal and Jastrow terms in the JAGP: we estimate the dynamical contribution to the binding energy of the order of 1.4(0.2) Kcal/Mol whereas the covalent one about 1.0(0.2) Kcal/Mol. JAGP reveales thus a promising WF for describing systems where dispersive and covalent forces play an important role

12:27PM Q26.00007 Hydrogen bond network ordering of liquid water confined between two metallic plates studied by ab initio molecular dynamics , MARIVI FERNANDEZ-SERRA, Physics & Astronomy SUNY, Stony Brook — We present an ab initio molecular dynamics study of liquid water confined between two palladium h111i surface slabs, at room temperature. We analyze in detail the layering and ice-Ih-type ordering of water molecules close to the metal interfaces. In particular we show how water molecules next to the metal surface display a very different structural and dynamic behavior as compared those in the “bulk” regions, which can be easily characterized using infra-red spectroscopy. Hydrogen bonds near the metallic interfaces are strengthen, inducing a characteristic ordering which decays with de distance from the surfaces. Our preliminary results show that this confined water presents an asymmetrical and stable structure as a function of Z (axis perpendicular to the surfaces) which results in a characteristic system with an overall ordering of the water molecules resembling that of ferroelectric systems.

12:39PM Q26.00008 Quasiparticle lifetime and edge localized states of graphite studied by high-resolution ARPES , KATSUAKI SUGAWARA, TAKAFUMI SATO, SEIGO SOUMA, TAKASHI TAKAHASHI, Tohoku University, HIROHITO SUEMATSU, RIKEN, Spring-8 — We have performed an ultrahigh-resolution angle-resolved photoemission spectroscopy (ARPES) of high-quality graphite single crystal (kish graphite) to elucidate the band structure and many-body interaction. We clearly observed an extremely small hole-like Fermi surface centered at the 1 K(H) point, a sharp quasiparticle peak in the vicinity of the Fermi level (EF ), and a kink in the dispersin at 0.18 eV. We also found ﬁrst evidence for the edge localized states near EF , whose energy dispersion is markedly diﬀerent from that of the bulk band. We will discuss the energy- and temperature-dependence of quasiparticle lifetime in relation to the strong electron-phonon coupling, the electron-plasmon interaction, and the electron-hole pair excitations. 1K. Sugawara et. al., Phys. Rev. Lett. 98 (2007) 036801. 2K. Sugawara et. al., Phys. Rev. B 73 (2006) 045124.

12:51PM Q26.00009 Fully ab-initio study of the optical response of charged rare gas clusters1 , FERNANDO NOGUEIRA, Center for Computational Physics and Physics Department, University of Coimbra, Portugal, MICAEL OLIVEIRA, Center for Computational Physics, University of Coimbra, Portugal and European Theoretical Spectroscopy Facility, MIGUEL MARQUES, LPMCN, UniversitéLyon I, Lyon, France and European Theoretical Spectroscopy Facility — Charged rare-gas clusters are markedly different from their neutral, van der Waals bonded counterparts. The removal of an electron from a strongly antibonding orbital causes the bonding to become much stronger and shifts the optical absorption to the visible region. We report a fully ab-initio determination of the geometry, electronic structure, and optical response of small singly charged Ne, Ar, Kr and Xe clusters. All calculations were performed using a pseudopotential based real space implementation of Time-Dependent Density-Functional Theory. We find that GGA leads, in general, to much better results than LDA, even though it predicts some absorption peaks at slightly higher energies than those found experimentally. The lighter elements show a single absorption peak but in the heavier elements spin-orbit interaction induces a splitting of the absorption peak, in good agreement with experiment.

1This work was supported by Funda¸cãopara a Ciência e Tecnologia through grants #POCI/FIS/58309/2004 and #SFRH/BD/12712/2003. 1:03PM Q26.00010 Continuous fluorescence from single colloidal semiconductor nanocrystals , XIAOYONG WANG, MEGAN HAHN, TODD KRAUSS, Department of Chemistry, University of Rochester, New York, 14627, KEITH KAHEN, XIAOFAN REN, MANJU RAJESWARAN, Eastman Kodak Company, Rochester, New York 14650, UNIVERSITY OF ROCHESTER TEAM, EASTMAN KODAK COMPANY COLLABORATION — Photoluminescence (PL) intermittency, or “blinking”, first discovered for single CdSe colloidal nanocrystals (NCs) a decade ago, has been established as an intrinsic and unavoidable property of all colloidal semiconductor NCs. Indeed, fluorescence blinking is generally accepted as the hallmark of single fluorophore emission. By judicious synthesis of a semiconductor shell of ZnSe around a CdSe NC, we were able to completely suppress PL blinking in these NCs on time scales from milliseconds to hours. Interestingly, these NCs have a radiative lifetime of about 5 ns, 3-4 times smaller than the value routinely measured from traditional CdSe NCs. Finally, single particle PL spectra are highly unusual, and display three peaks separated by about 160 meV. Possible mechanisms for the non-blinking behavior, the short radiative lifetime, and the multiple emission peaks will be discussed.

1:15PM Q26.00011 ABSTRACT WITHDRAWN —

1:27PM Q26.00012 Cubic Nonlinearity of Ag/Au Coreshells , SEONGMIN MA, JAETAE SEO, QIGUANG YANG, BAGHER TABIBI, DOYLE TEMPLE, Hampton University, WANJOONG KIM, JINHA HEO, WAN SOO YUN, SUNGSOO JUNG, Korea Research Institute of Standards and Science, HAMPTON UNIVERSITY COLLABORATION, KOREA RESEARCH INSTITUTE OF STANDARDS AND SCIENCE COLLABORATION — Cubic nonlinearity of Ag/Au spherical coreshells in toluene were investigated by polarization-resolved degenerate four-wave mixing with 6-ns laser pulse at 532 nm with 10-Hz repetition. The average diameter of Ag core was ∼6.7 nm. The overall diameter of Ag/Au was changed from 6.1 to 9.1 nm by adding more mole concentration of HAuCl4, which resulted in the change of surface plasmon resonance peaks from 411 to 492 nm. The hyperpolarizability of Ag/Au coreshells with parallel and orthogonal excitations were changed from ∼3.4×10−38 to ∼2.7×10−40 m5/V2 and from ∼2.5×10−38 to ∼1.1×10−40 m5/V2, respectively, as the shell thickness of Au was increased. It implies that dephase or decay rates of materials have main contributions on cubic nonlinearity rather than excitation cross-section. This work at Hampton University was supported by Army Research Oﬃce (W911NF-07-1-0608) and National Science Foundation (HRD-0734635, HRD-0630372, ESI-0426328/002, and EEC-0532472).

1:39PM Q26.00013 Tracking Nanocars Using Single Molecule Spectroscopy , STEPHAN LINK, SAUMYAKANTI KHATUA, KEVIN CLAYTOR, JASON GUERRERO, JAMES TOUR, Rice University — Nanocars belong to an exciting new class of molecules known as molecular machines. They consist of four fullerene or carborane wheels attached to a chassis consisting of a stiff aromatic backbone. The nanocars are designed to roll over a solid surface making them potential candidates for nano-cargo transporters. Here, we present our results on tracking of nanocars by single molecule fluorescence spectroscopy. By attaching the fluorescent tag tetramethylrhodamin isothiocyanate to the nanocars, we were able to visualize and track individual nanocars using confocal sample scanning microscopy. Fluorescence images were analyzed for directional movement as opposed to random diffusion or stage drift. We had to overcome 2 major problems in our image analysis: 1) fluorescence photo-blinking and 2) photo-bleaching. We developed routines that are capable of tracking individual fluorescent molecules while accounting for photo-blinking and photo-bleaching. The ability to track individual nanocars is checked independently by simulations. Our method is not limited to tracking of nanocars however, and can be extended to follow individual molecules in biological or mechanical systems as well.

1:51PM Q26.00014 Time-resolved photoluminescence Studies of CdSe Core and CdSe/ZnS Core/Shell colloidal nanoparticles as function of temperature and concentration , M. YASAR, A. ANTIPOV, M. BELL, V. MITIN, A. VEREVKIN, Department of Electrical Engineering, SUNY at Buffalo, Buffalo, NY 14260, A. PETROU, Department of Physics, SUNY at Buffalo, Buffalo, NY 14260 — We report the results of time-resolved photoluminescence studies (TRPL) of CdSe Core and CdSe/ZnS Core/Shell colloidal nanoparticles dissolved in toluene in the temperature range of 10-300 K. The integrated PL intensity of nanoparticles in liquid changes little between 10 K and 300 K, whereas the intensity of the “dry” nanoparticles quenches dramatically as temperature is increased. The PL exhibits biexponential decay characteristics; the longer decay component is affected by the presence of the solvent. In particular, the phase transitions (the glass-solid and the solid-liquid) of the solvent are clearly detected by our experiment. In addition, the PL efficiency and decay times are studied as a function of nanoparticle concentration. Our findings suggest that the PL quantum yield as well as the decay times strongly depend on the solvent temperature, as well as nanoparticles concentration. These results are discussed in terms of reabsorption and reemission between nanoparticles. We acknowledge support of NSF IGERT, NYSTAR and ONR.

2:03PM Q26.00015 Photon-Correlation Fourier Spectroscopy on CdSe Nanocrystals , LISA MAR- SHALL, Massachusetts Institute of Technology, XAVIER BROKMANN, Capital Fund Management, MOUNGI BAWENDI, Massachusetts Institute of Technology — The emission spectrum of a single emitter can be artificially widened and blurred due to fluctuations in emission energy, i.e. spectral diffusion. This spectral diffusion can be much more rapid than the time required to collect sufficient photons to measure a spectrum. We use a new method, Photon-Correlation Fourier Spectroscopy (PCFS), to “freeze” spectral diffusion and obtain spectral information of single CdSe nanocrystals on timescales comparable to the lifetime of the emitter. This method cross-correlates the two outputs of a Michelson interferometer, providing a histogram of frequency shifts between two photons separated by a given amount of time. We apply PCFS to single nanocrystals in a confocal geometry. We also combine PCFS with Fluorescence Correlation Spectroscopy (FCS) to resolve single nanocrystal linewidths from a solution of nanocrystals diffusing under a microscope objective.

Wednesday, March 12, 2008 2:30PM - 5:30PM — Session S13 DCOMP DCP: Focus Session: Frontiers in Electronic Structure Theory I Morial Convention Center 204 2:30PM S13.00001 Total and self-energies beyond LDA and GGA: exact-exchange, GW and MP2 united by numeric atom-centered orbitals , XINGUO REN, ANDREA SANFILIPPO, ALEXANDRE TKATCHENKO, Fritz Haber Institute, Berlin, Germany, PATRICK RINKE, Univerisity of California at Santa Babara, CA, VOLKER BLUM, KARSTEN REUTER, MATTHIAS SCHEFFLER, Fritz Haber Institute, Berlin, Germany — Well-known deficiencies of (semi-)local exchange correlation functionals in density functional theory comprise the spurious self-interaction, the absence of long-range correlation, and the absence of the derivative discontinuity with respect to the electron number. Present approaches to overcome these deficiencies (e.g., hybrid functionals, MP2, and GW) typically involve expensive two-electron Coulomb repulsion integrals. For molecules, the resulting numerical effort usually restricts these methods to Gaussian basis functions. We here show how all these methods can be handled accurately with efficient all-electron numerical atom-centered basis sets [1], by using a second, auxiliary basis for products of basis functions (resolution of the identity). For an extended set of finite systems spanning small molecules (water dimer, benzene), metal clusters (Nan) and biomolecules (polyalanine peptides), we demonstrate that the efficiency of optimized numeric atom-centered basis sets is directly carried over into our new approach. Our approach is then applied to analyze the CO-adsorption problem (CO/Cu(111)). [1] V. Blum et al., The FHI-aims project, www.fhi-berlin.mpg.de/aims 2:42PM S13.00002 Order N Implementation of Exact Exchange , XIFAN WU, Princeton University, ANNABELLA SELLONI, ROBERTO CAR — Exact (Hartree Fock) exchange is needed to overcome some of the limitations of local and semilocal approximations of density functional theory (DFT). Moreover exact exchange is a basic ingredient in modern approaches to compute excitation properties, like the GW and the OEP schemes. So far, however, computational cost has limited the use of exact exchange in plane wave calculations for extended systems. We show that this difficulty can be overcome by performing a unitary transformation from Bloch to Maximally Localized Wannier functions in combination with an efficient technique to compute real space Coulomb integrals. The resulting scheme scales linearly with system size and, when used in ab-initio molecular dynamics simulations, requires only a modest increase in computational cost compared to standard DFT implementations. We validate the scheme with representative applications.

2:54PM S13.00003 Accurate and fast DFT calculations with the AM05 functional , ANN E. MATTS- SON, Sandia National Laboratories, Albuquerque NM 87185-1322 — The AM05 functional [1] has the same excellent performance for solids as the hybrid density functionals tested in Paier et. al. (J. Chem. Phys 124, 154709 (2006); ibid 125, 249901 (2006)). This confirms the original finding that AM05 performs exceptionally well for solids and surfaces. While hybrid functionals are computationally expensive, preveting them from being used in large systems and/or long molecular dynamics simulations, the AM05 functional is on a regular semi-local GGA form with corresponding computational cost. The performance of AM05 is even superior to an ‘informed choice’ between LDA and PBE. By comparing data from different electronic-structure codes we have determined that the numerical errors in this study are equal to or smaller than corresponding experimental uncertainties. Results for other systems will also be presented. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000. [1] R. Armiento and A. E. Mattsson, Phys. Rev. B 72, 085108 (2005).

3:06PM S13.00004 Beller Lectureship Talk: Exploring Exact Exchange for collinear and non- collinear magnetism1 , CLAUDIA AMBROSCH-DRAXL, University of Leoben — In standard density functional theory, one usually describes exchange and correlation effects by approximations on the same footing, where typical examples are the local density approximation (LDA) and different flavours of the generalized gradient approximation (GGA). Only in recent years the exact exchange (EXX) or optimized effective potential (OEP) method has been investigated in more detail, where most of the work has been dedicated to semiconductors [1]. Here we explore the OEP approach for magnetic materials. We provide a general description of the method which comprises the case of non-collinear magnetism. The equations for the effective Kohn-Sham scalar potential and magnetic field are derived within this framework, where the exact exchange energy functional explicitly depends on two-component spinor orbitals. The example of a magnetically frustrated Cr monolayer shows [2] that the resulting magnetization density exhibits much more non-collinear structure compared to LDA. The finding that a time-dependent generalization of the non-collinear OEP method can be a promising approach for an ab-initio description of spin dynamics provides an interesting outlook for future work. In the present study, a series of materials is investigated in view of the reliability of the OEP method in terms of their magnetic properties. [1] M. Städele, M. Moukara, J. A. Majewski, P. Vogl, and A. Görling, Phys. Rev. B 59, 10031 (1999). [2] S. Sharma, J. K. Dewhurst, C. Ambrosch-Draxl, N. Helbig, S. Kurth, S. Shallcross and L. Nordström,and E. K. U. Gross, Phys. Rev. Lett. 98, 196405 (2007).

1Work supported by the Austrian Science Fund.

3:42PM S13.00005 A GGA+U approach to realistic modeling of transition-metal complexes , HEATHER KULIK, NICOLA MARZARI, DMSE, Massachusetts Institute of Technology — Despite the importance of transition metal centers in a variety of biological and inorganic chemical reactions, density functional theory calculations often fail quantitatively in describing both the stable intermediate electronic structures, splittings, and geometries as well as reaction barriers and geometries of transition states. We have shown1 that augmenting the generalized-gradient approximation (GGA) with a Hubbard U which is obtained from a self-consistent linear response procedure can greatly improve the description of both spin state splittings in the iron dimer as well as reaction barriers in the addition-elimination reaction of hydrogen and methane with FeO+. This fully ab-initio GGA+U approach provides excellent agreement with accurate, correlated-electron quantum chemistry calculations but at a fraction of the cost of these methods. We will further highlight how our method aﬀords substantial improvement in the physical description of hybridization and bonding irrespective of system size. We thus fruitfully employ GGA+U in the study of large-scale complexes which contain hundreds of atoms such as the active site of halogenating enzymes and various porphyrin complexes. 1 H. J. Kulik, M. Cococcioni, D. Scherlis and N. Marzari, PRL 97 103001, (2006).

3:54PM S13.00006 Accurate description of the bonding of C6H6 at noble metal surfaces, using a local exchange-correlation correction scheme , ERIK MCNELLIS, KARSTEN REUTER, MATTHIAS SCHEFFLER, Fritz-Haber- Institut der MPG — The adsorption of benzene (C6H6) at the Cu(111) surface is a much studied model system for the interaction of larger π-conjugated molecules with solid surfaces. At first glance a simple system, the suspected predominantly van der Waals type bonding at the extended metal surface poses a severe challenge for accurate first-principles calculations. Density-Functional Theory (DFT) with local and semi-local exchange-correlation (xc) functionals is uncertain to properly account for this type of bonding, while the system sizes required to correctly grasp the metallic band structure are computationally untractable with correlated wave function techniques. We overcome these limitations with a recently introduced “local xc correction” scheme [1], correcting the adsorption energetics from present-day DFT xc functionals with hybrid functional and Møller-Plesset perturbation theory calculations for small clusters. From the obtained convergence of the xc correction with cluster size we can disentangle short-range and dispersion type contributions to the bonding of the molecule at different heights above the surface. This enables us to qualify the role played by the two contributions in determining the binding energetics and geometry. [1] Q.-M. Hu, K. Reuter, and M. Scheffler, PRL 98, 176103 (2007) and 99, 169903 (2007); C. Tuma and J. Sauer, CPL 387, 388 (2004).

4:06PM S13.00007 Transcorrelated method applied to covalent and ionic solids: total energy and band structure calculation , KEITARO SODEYAMA, SHINJI TSUNEYUKI, Department of Physics, University of Tokyo, REI SAKUMA, JST-CREST, AIST — To calculate the electronic structures of solids including electron correlation eﬀects, we have developed the transcorrelated (TC) method which was ﬁrst proposed by Boys and Handy. In the TC method, the wave function is represented by a correlated wave function F Φ, where Φ is a single Slater determinant and F is a Jastrow function, F = exp[− P u ]. u is a two-body function called Jastrow factor. The many-body Hamiltonian H is similarity i

4:30PM S13.00009 RPA Correlation Energy in ACFD Formalism with Thomas-Fermi-von Weizsäcker Approximation , VIET HUY NGUYEN, STEFANO DE GIRONCOLI, Intl School for Adv Studies (SISSA), Trieste Italy — It is well known that LDA or GGAs approximations in DFT do not describe correctly systems where long range correlations are important. In the Adiabatic Connection Fluctuation-Dissipation (ACFD) formalism correlation energy can be computed accurately from Kohn-Sham and interacting linear response functions. Although computationally very demanding, this formalism has shown to describe correctly systems where standart DFT fails qualitatively by combining RPA xc-kernel with short-range local-density corrections (RPA+). On the other hand, Thomas-Fermi-von Weizsäcker approximate kinetic response function can capture reasonably well asymptotic long range interactions via van der Waals coefficients, and has the computationally desirable feature that it only involves a single auxiliary wavefunction regardless of the number of electrons in the system. Here, we show how to use this approach to calculate approximate RPA correlation energies. Numerical results for atoms show that this approach gives approximate RPA correlation energies closer to the experimental values than those obtained by full RPA and, when combined with a short-range local-density correction, it gives results at least as good as those of full RPA+. The possibility is therefore open to address large systems where correlations need to be treated beyond LDA and GGAs.

4:42PM S13.00010 Generalized density functional theory for effective potentials in many-body electronic structure , F. A. REBOREDO, P. R. C. KENT, Oak Ridge National Laboratory — We demonstrate the existence of different density functionals that retain selected properties of the many-body ground state in the non-interacting density functional solution. We focus on diffusion Monte Carlo applications that require trial wave functions with Fermion optimal nodes. The theory can be extended and used to understand current practices in several electronic structure methods [GW-BSE,CI,EPM] within a generalized density functional framework. The theory justifies and stimulates the search of optimal empirical density functionals and effective potentials but also cautions on the limits of their applicability. The theoretical concepts are tested against a near-analytic model that can be solved to numerical precision. Research performed at the Materials Science and Technology Division and the Center of Nanophase Material Sciences at Oak Ridge National Laboratory sponsored the Division of Materials Sciences and the Division of Scientific User Facilities U.S. Department of Energy.

4:54PM S13.00011 Towards QMC benchmarks for large scale dispersive interactions1 , JONATHAN L DUBOIS, RANDOLPH Q. HOOD, SEBASTIEN HAMEL, ERIC R. SCHWEGLER — Fixed-node quantum Monte-Carlo (QMC) methods are becoming an increasingly attractive approach for the study of large scale problems in electronic structure. Current challenges lie in efficient application of QMC to large (thousands of electrons) systems and removal or amelioration of the uncontrolled approximations inherent in most practical applications of the method. I will present recent progress and address some of the particular challenges associated with the development of exact potential energy surfaces for weakly interacting closed shell carbon complexes within the fixed-node QMC ansatz. In particular, the efficacy / necessity of backflow corrections and multi-determinant expansions as a method for optimizing the nodal surface in these systems will be discussed.

1This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52- 07NA27344.

5:06PM S13.00012 Real or artifactual symmetry breaking in BNB: A fixed-node diffusion Monte Carlo study1 , WISSAM A. AL-SAIDI, CYRUS UMRIGAR, Cornell University — The linear BNB molecule represents one of the most challenging examples of symmetry-breaking effects because of its susceptibility to a second-order Jahn-Teller distortion along the antisymmetric stretching mode. This real symmetry breaking could be confused in calculations with an artifactual one caused by the approximate nature of the theoretical approach. Thus the debate of whether the ground state of BNB is symmetric in the positions of the boron atoms with respect to nitrogen or if this symmetry is broken. Our preliminary investigations with diffusion Monte Carlo shows that the symmetric and the broken symmetry geometries are nearly degenerate, which would suggest a highly floppy quasi-symmetric BNB ground state.

1Supported by NSF and DOE.

5:18PM S13.00013 Potential Energy Curves and Excited States of the C2 Molecule by Auxiliary-Field Quantum Monte Carlo (AFQMC)1 , WIRAWAN PURWANTO, HENRY KRAKAUER, SHIWEI ZHANG, College of William and Mary, WISSAM AL-SAIDI, Cornell University — The accurate determination of potential energy curves (PECs) and excited states represents two difficult problems in electronic structure calculations. We present AFQMC PECs of the challenging C2 molecule, focusing on the ground state and two singlet low-lying excited states. AFQMC calculates a target many-body wave function (WF) by means of random walks in the space of Slater determinants. 2 We employ truncated complete active space (CAS) trial WFs (ΨT ) to guide the AFQMC projection to obtain the desired state. With the phase-free constraint, the CAS ΨT is effective in controlling the sign/phase problem, and filtering in the desired excited state. The AFQMC results are in very good agreement with exact results. Comparison with experimental spectroscopic constants will also be presented.

1Supported by DOE CMSN, ONR, NSF, and ARO. Calculations were performed at the CPD and W&M SciClone. 2S. Zhang and H. Krakauer, Phys. Rev. Lett. 90, 136401 (2003)

Wednesday, March 12, 2008 2:30PM - 5:18PM — Session S21 DCP: Focus Session: Fundamental Issues in Catalysis III Morial Convention Center 213 2:30PM S21.00001 Transient FTIR spectroscopy for probing reaction pathways on Au catalysts1 , STEVEN H. OVERBURY, Oak Ridge National Laboratory — Au is now well known to be an active catalyst if the Au particles are sufficiently small, less than about 5 nm. The causes for this structure sensitivity are now beginning to be better understood. Computational modeling and measurements of size dependence on a single catalyst are consistent with activity at sites with low coordination numbers, due in part to flexibility of adsorbate geometry in these sites. Although small size and low coordinate sites are important in catalyzing, e.g. the CO oxidation reaction, there appear to be other factors which control the observed activity as demonstrated by catalyst deactivation and unusual temperature dependence. We have performed studies of CO oxidation over Au/TiO2, Au/SiO2, Au/ZnO/TiO2 and Au/FePO4 catalysts to explore reaction pathways and the causes for activation and deactivation. Three different reactor systems, a fast gas transient FTIR spectrometer, a slower transient DRIFTS cell and a steady state plug flow reactor have been used to correlate activity with surface species. Using this operando approach the elementary steps in the CO oxidation reaction have been explored. Striking differences between the supports are found. The effect of various pre-treatments, the evolution of the surface species during “steady state” reaction and the role of carbonate, oxygen storage, water, hydroxyl upon catalyst activation and deactivation have been explored and will be described. Reaction pathways and mechanisms will be proposed and compared for the different catalysts.

1Research sponsored by the Division of Chemical Sciences, Geosciences, and Biosciences, Oﬃce of Basic Energy Sciences, U.S. Department of Energy.

3:06PM S21.00002 TBD , BRIAN HAYDEN, University of Southampton — No abstract available.

3:42PM S21.00003 Molecular Factors Determining Selectivity in Catalysis.1 , FRANCISCO ZAERA, University of California — Achieving high selectivities is arguably the main challenge in heterogeneous catalysis for the 21st century. In complex reaction with competing parallel pathways, small changes in the relative values of the different activation energies are sufficient to switch the selectivity of those processes from one product to another. We in our laboratory have been carrying out mechanistic studies on model metal surfaces to try to identify the key factors that control such selectivity. In this talk we will present several examples of increasing subtlety from that work, with focus on the conversion of hydrocarbons. Specifically, we will discuss issues of regioselectivity and stereoselectivity in early dehydrogenation steps, and how those affect selectivity in the conversion of olefins. Time permitting, we will also discuss issues related to the bestowing of enantioselectivity on solid surfaces.

1Research funded by the US National Science Foundation and Department of Energy

4:18PM S21.00004 The nucleation and growth of ordered Fe and FeO nanoparticles on reconstructed Au(111) surfaces , NEETHA KHAN, CHRISTOPHER MATRANGA, U.S. Dept. of Energy — Iron-based catalysts, including iron oxides, are an important class of materials with relevance to Fischer-Tropsch catalysis and gas-sensing applications. By growing nanostructured particles on single-crystal surfaces, we can create a model system to study size and shape effects on reactivity. We have studied the formation of monolayer thick iron oxide nanoparticles and thin films on the reconstructed Au(111) surface. STM, XPS, ISS, and LEED were used to evaluate the structure and composition of the iron oxide nanoparticles and films as a function of growth conditions. Iron oxide was grown by depositing iron on Au(111), followed by oxidation at room temperature and annealing to 700 K. XPS results indicate that the Fe is oxidized at room temperature, but the STM results indicate that the particles are not ordered until after annealing to 700 K. Atomically-resolved STM images show that at 0.3 ML Fe coverage, iron oxide nanoparticles, pseudo-hexagonal in shape are formed, with large defects occurring in the corners. STM images of FeO particles over 0.5 ML Fe also show evidence of a non-coincidence overlayer lattice with a short periodicity of 0.25-0.3 nm modulated by a larger periodicity of approximately 3.5 nm. The larger periodicity results from a moirépattern formed between the iron oxide overlayer and the underlying Au(111) surface.

4:30PM S21.00005 Dynamic structure in Pt nanoclusters on γ-alumina1 , F. VILA, J.J. REHR, J. KAS, Dept. of Physics, U. of Washington, R.G. NUZZO, Dept. of Chemistry, U. of Illinois at Urbana-Champaign, A.I. FRENKEL, Yeshiva U. — Pt nanoclusters on γ-alumina exhibit a number of unusual phenomena including large structural disorder and bond-length contraction with increasing temperature. We investigate this behavior for a prototypical 10-atom Pt cluster using real-time, temperature-dependent simulations combining density functional theory/molecular dynamics and x-ray spectroscopy theory. We ﬁnd that the cluster structure is dynamically varying in shape and topology on a time scale long compared with internal vibrations. Moreover, the clusters are not rigidly attached to the surface and occasionally pick up or discard a Pt-O bond. This real-time approach suggests that these nanoclusters are comprised of two distinct populations of Pt atoms depending on the charge transfer from the surface, and reproduces many of their unusual properties.

1Supported by DOE Grants DE-FG02-04ER1599 (FV and JJR), DE-FG03-97ER45623 (JJR), DE-FG02-03ER15476 (RGN and AIF), and NIH NCRR BTP Grant No. RR-01209 (JJK), and by DOE computer support at NERSC.

4:42PM S21.00006 In Situ Characterization of Ethylene Hydrogenation on Pt Powder Using Mass Spectrometry-Sum Frequency Generation Technique , BRYAN HSU, Department of Chemistry, Massachusetts Institute of Technology, SHAWN DOUGAL, PAUL STEVENS, MOHSEN YEGANEH, Exxonmobil Research and Engineering Company, Corporate Strategic Research — Bridging the pressure gap has been of paramount importance to the field of surface science. Unfortunately, the available techniques used to characterize catalytic surfaces have all been limited in some degree by a combination of factors (e.g. low pressure regimes, ex situ analysis, and low surface area catalysts), which do not fully replicate industrially relevant conditions. Here, we present in situ observation of ethylene hydrogenation of Pt powder in a high pressure regime. Using total internal reflection sum frequency generation (TIR-SFG) we are able to identify ethyl, ethylidyne, di-sigma-bonded ethylene, and pi-bonded ethylene surface intermediates and find that these are all present under reactive conditions as monitored with mass spectrometry (MS).

4:54PM S21.00007 Dissociation of water and Acetic acid on PbS from first principles1 , ALESSANDRA SATTA, PAOLO RUGGERONE, CNR-INFM SLACS, GIOVANNI DE GIUDICI, Dept. Earth Science, University of Cagliari — The adsorption of complex molecules at mineral surfaces are crucial ingredients for understanding the mechanisms that rule the interaction between minerals and the biosphere and for predicting both the stability and the reactivity of minerals. The present work focuses mainly on the early stages of different adsorption reactions occurring at both the cleavage surface and a high-index vicinal surface of galena (PbS). We have studied the dissociation mechanism of water and acetic acid on the galena surfaces by means of ab initio calculations within the framework of the density functional theory in the generalized gradient approximation and of pseudopotential approach. The calculated adsorption energies of the molecules indicate the stepped surface as the most reactive, as expected. The free energy surface during the reaction process has been explored via metadynamics[1]. The optimized configurations of both reactants and products obtained, were then used to accurately calculate the dissociation energy via the Nudge Elastic Band method[2]. [1] A. Laio and M. Parrinello, PNAS 99, 12562 (2002). [2] G. Mills and H. Jonsson, Phys. Rev. Lett. 72, 1124 (1994).

1A.S. and P.R. thank CASPUR and CyberSar for computing support and Fondazione Banco di Sardegna for partial ﬁnancial support. + 5:06PM S21.00008 Characterization and Reactivity of Mo6S8 on Au (111) via Size-Selected Deposition , MELISSA J. PATTERSON, JAMES M. LIGHTSTONE, StonyBrook University, MICHAEL G. WHITE, Brookhaven National Labora- tory/StonyBrook University — Supported MoS2 nanoparticles are known for their ability to catalyze a wide range of heterogenous reactions such as hydrodesul- 1 furization (HDS) . However, understanding the role of size, structure, composition and support interactions of the MoS2 particles in these heterogenous reactions has not yet been resolved due to the inhomogeneity of commercial catalysts. Work done in our laboratory is geared towards preparing homogenous samples in ultra high vacuum that can serve as model systems for these types of catalytic reactions. We are currently investigating the reactivity of size-selected transition metal clusters generated in the gas-phase and deposited on a Au(111) surface. Using a magnetron cluster source, we are able to produce a wide + 2 range of nanocluster stoichiometries including the Mo6S8 cluster, which has been observed as the metal core of the well-known Chevrel phase . The work + presented focuses on characterization of the Mo6S8 cluster deposited on a Au(111) single crystal using techniques such as Auger, photoemission spectroscopy, + and thermal desorption. In addition, preliminary reactivity studies will be presented of the supported Mo6S8 cluster with small sulfur containing molecules. 1. Topsoe, H.; et.al; Hydrotreating Catalysis; Springer: New York, 1996. 2. Umarji, A. M.; et.al.; J. Phys. Chem. Solids 1980, 41, 421.

Wednesday, March 12, 2008 2:30PM - 4:54PM — Session S26 DCP: Focus Session: Advances in Atmospheric Aerosol Science I Morial Convention Center 218

2:30PM S26.00001 Tropopsheric Aerosol Chemistry via Aerosol Mass Spectrometry , DOUGLAS WORSNOP1, Aerodyne Research, University of Helsinki — A broad overview of size resolved aerosol chemistry in urban, rural and remote regions is evolving from deployment of aerosol mass spectrometers (AMS) throughout the northern hemisphere. Using thermal vaporization and electron impact ionization as universal detector of non-refractory inorganic and organic composition, the accumulation of AMS results represent a library of mass spectral signatures of aerosol chemistry. For organics in particular, mass spectral factor analysis provides a procedure for classifying (and simplifying) complex mixtures composed of the hundreds or thousands of individual compounds. Correlations with parallel gas and aerosol measurements (e.g. GC/MS, HNMR, FTIR) supply additional chemical information needed to interpret mass spectra. The challenge is to separate primary and secondary; anthropogenic, biogenic and biomass burning sources - and subsequent - transformations of aerosol chemistry and microphysics.

1In collaboration with: Tim Onasch, Manjula Canagaratna, John Jayne, Jesse Kroll, Achim Trimborn, Aerodyne Research; Ingrid Ulbrich, Allison Aiken, Peter DeCarlo, Jose Jimenez University of Colorado; Qi Zhang, SUNY Albany.

3:06PM S26.00002 The Dynamic Interaction of Chemistry and Phase Partitioning in At- mospheric Organic Aerosols1 , NEIL DONAHUE, Carnegie Mellon University — Atmospheric organic aerosols are a dynamic, chemically evolving mixture in equilibrium between the gas and condensed phases. This applies equally to primary emissions, which span a huge range in volatility, as well as secondary oxidation products generated by chemical reactions in both phases. The degree of volatility of primary emissions has been historically underappre- ciated, and the role of oxidation reactions has been considered in almost all cases only through their ﬁrst one or two generations. We have recently developed a ‘volatility basis set’ to address both primary volatility distributions and secondary volatility evolution (sometimes called primary organic aerosol and secondary organic aerosol). Here we shall discuss both facets of this framework as they apply to problems in organic aerosols on all scales, from emissions measurements to global organic aerosol loadings. We shall describe ongoing experimental work to constrain volatility distributions and volatility evolution through chemistry as well as extensions to the basis-set framework to more fully describe evolving aerosol properties.

1In collaboration with Allen Robinson, Carnegie Mellon University.

3:42PM S26.00003 Tandem mass spectrometry of single organic aerosol particles: A promising approach for in-situ analysis of mixtures. , PEDRO CAMPUZANO JOST, SARAH HANNA, EMILY SIMPSON, DAMON ROBB, MICHAEL BLADES, JOHN HEPBURN, ALLAN BERTRAM, University of British Columbia — We have built a new single particle mass spectrometer for organic aerosol analysis that combines different previously tried approaches into one single instrument. We use soft, wavelength tunable desorption by using a dedicated pulsed CO2 laser, (Prather, Baer & coworkers) and soft ionization by tunable VUV radiation (Baer, Wilson & coworkers)) to ensure a minimum of fragmentation. By ionizing the aerosol plume in the center of an ion trap both high sensitivity and the ability to elucidate structure by tandem mass spectrometry (Reilly & coworkers) can be achieved. The analytical performance of the instrument as well as the detection geometry has first been validated by using simpler ionization techniques, 70 eV EI and REMPI, on a suite of aromatic and aliphatic compounds and simple mixtures. The novel tunable VUV laser system has been thoroughly characterized with a host of gaseous organic compounds that has proven both the ability to determine ionization energies with high accuracy and the possibility in many cases to minimize fragmentation by tuning the VUV source close to the ionization threshold. The VUV source has been integrated into the aerosol mass spectrometer and first VUV single aerosol spectra will be presented.

3:54PM S26.00004 A novel flow reactor for studying the hydrolysis of N2O5 on aqueous H2SO4 solutions coated with organic surfactants , DANIEL KNOPF, Institute for Terrestrial and Planetary Atmospheres, Stony Brook University, LORI COSMAN, ALLAN BERTRAM, Dept. of Chemistry, UBC, PAYAM MOUSAVI, SATYA MOKAMATI, Dept. of Mech. Eng., UBC — A flow reactor has been developed which allows the study of heterogeneous kinetics on an aqueous surface coated by organic monolayers. Computational fluid dynamics simulations have been used to determine the flow characteristics for various experimental conditions. A mathematical framework has been developed to derive the true first order wall loss rate coefficient from the experimentally observed wall loss rate. Validation of the flow reactor was performed by measuring reactive uptake coefficients of well studied systems as a function of flow velocity and pressure. We determined the reactive uptake of N2O5 on aqueous H2SO4 solutions coated with a monolayer of 1-octadecanol, 1-hexadecanol, stearic acid, and phytanic acid. The reactive uptake decreased by approximately a factor of 17–61 in the presence of insoluble, straight-chain organic monolayers compared to uncoated solutions. However, the branched monolayer (phytanic acid) did not significantly affect the N2O5 uptake. The reactive uptake coefficients measured on aqueous H2SO4 subphases show a relationship to the surface area occupied by the surfactant molecules. However, data obtained with other subphases do not overlap with this trend.

4:06PM S26.00005 Spectromicroscopic Studies of the Aging of Carbonaceous Aerosols from Mexico City , RYAN MOFFET, Lawrence Berkeley National Laboratory, YURY DESYATERIK, Pacific Northwest National Laboratory, ALEXI TIVAN- SKI, University of Iowa, REBECCA HOPKINS, Defense Science and Technology Laboratory, JEROME FAST, JAMES BARNARD, ALEXANDER LASKIN, Pacific Northwest National Laboratory, MARY GILLES, Lawrence Berkeley National Laboratory — Milagro, a multi-national atmospheric field campaign, was conducted in Mexico City during March of 2006. Aerosols were collected at three ground based sites, situated progressively farther from the city center. These aerosol samples are studied with computer controlled scanning electron microscopy with energy dispersive X-ray analysis (CCSEM/EDX) and scanning transmission x-ray microscopy with near edge X-ray absorption fine structure spectroscopy (STXM/NEXAFS). This presentation focuses on evidence for carbonaceous aerosol transformation examining aerosol composition, C/O atomic ratios, mixing states, and changes in carbon bonding over time and distance from the source. 4:18PM S26.00006 A connection between arctic haze and halogen chemistry? , PAUL SHEPSON, Purdue Climate Change Research Center — It has long been known that the Arctic spring time exhibits a phenomenon known as “Arctic Haze”, characterized by low visibilities, caused by a relatively high concentration of fine aerosol. This aerosol is known to be composed largely of sulfate, with the precursor SO2 transported from anthropogenic sources regions in North America and Eurasia. However, since the original studies of Arctic Haze, a complex array of halogen chemistry (involving Cl, Br and I chemistry), initiated by chemistry and photochemistry on frozen saline surfaces and in sea salt aerosol, has been discovered. That halogen chemistry makes the Arctic boundary layer extremely oxidizing, with large concentrations of both halogen radicals and HOx. That environment can lead to new particle production via oxidation of organic gas phase precursors and/or enhanced oxidation of SO2. Recent observations of a rapidly changing surface in the Arctic raise questions about how this halogen chemistry, which also which results in massive scale depletion of ozone and mercury, will change in the future. In this talk I will discuss what is known about halogen chemistry in polar regions, how that ties to aerosol chemistry, and how these are impacted by climate change and changes in the nature of the frozen surface.

Thursday, March 13, 2008 8:00AM - 11:00AM — Session U13 DCOMP DCP: Focus Session: Frontiers in Electronic Structure Theory II Morial Convention Center 204 8:00AM U13.00001 Self-consistent van der Waals density functional: Development and Appli- cations , VALENTINO COOPER, Rutgers University — The inability of density functional theory (DFT), with standard exchange-correlation functionals, to correctly describe van der Waals/dispersion (vdW) interactions has severely limited its applicability to sparsely packed systems, such as organic and biological molecules. Numerous attempts have been made to correct these deficiencies; however, many of them either require extensive reparameterization for each new situation or scale poorly with system size. In this paper, I will discuss the development and implementation of an exchange-correlation functional which correctly incorporates non-local vdW interactions within DFT (vdW-DF)1. In addition, I will present our recent development of the corresponding exchange- correlation 2 potential (Vxc) . The Vxc gives us the ability to compute Hellmann-Feynman forces, allowing for structural relaxations and molecular dynamics simulation. Using the Vxc I will examine the nature of the van der Waals bond between molecules. Finally, to demonstrate the power of the vdW-DF, I will discuss our relatively large scale application of the functional to study the influence of stacking interactions on the structure and stability of DNA. Here, I will show how these interactions are crucial for defining the twist and base pair separation in DNA and how methyl-nucleobase and methyl-methyl interactions give additional stability to DNA.

1M. Dion, H. Rydberg, E. Schr¨oder, B. I. Lundqvist and D. C. Langreth, Phys. Rev. Lett., 92, 246401 (2004) 2T. Thonhauser, V. R. Cooper, S. Li, A. Puzder, P. Hyldgaard, and David C. Langreth, Phys. Rev. B, 76, 125112 (2007)

8:36AM U13.00002 Stochastic Time-Dependent Current-Density Functional Theory1 , ROBERTO D’AGOSTA, University of California - San Diego — Static and dynamical density functional methods have been applied with a certain degree of success to a variety of closed quantum mechanical systems, i.e., systems that can be described via a Hamiltonian dynamics. However, the relevance of open quantum systems - those coupled to external environments, e.g., baths or reservoirs - cannot be overestimated. To investigate open quantum systems with DFT methods we have introduced a new theory, we have named Stochastic Time-Dependent Current Density Functional theory (S-TDCDFT) [1]: starting from a suitable description of the system dynamics via a stochastic Schr¨odingerequation [2], we have proven that given an initial quantum state and the coupling between the system and the environment, there is a one-to-one correspondence between the ensemble-averaged current density and the external vector potential applied to the system. In this talk, I will introduce the stochastic formalism needed for the description of open quantum systems, discuss in details the theorem of Stochastic TD-CDFT, and provide few examples of its applicability like the dissipative dynamics of excited systems, quantum-measurement theory and other applications relevant to charge and energy transport in nanoscale systems. [1] M. Di Ventra and R. D’Agosta, Physical Review Letters 98, 226403 (2007) [2] N.G. van Kampen, Stochastic processes in Physics and Chemistry, (North Holland, 2001), 2nd ed.

1Work supported by DOE grant DE-FG02-05ER46204

9:12AM U13.00003 Investigating interaction-induced chaos using time-dependent density functional theory , ADAM WASSERMAN, Harvard University — Systems whose underlying classical dynamics are chaotic exhibit signatures of the chaos in their quantum mechanics. In this talk I will discuss the possibility of using time-dependent density functional theory (TDDFT) to study the case when chaos is induced by electron interaction alone. Nearest-neighbor level- spacing statistics are in principle exactly and directly accessible from time-dependent density functional theory (TDDFT). Can the linear response formalism of TDDFT reveal the mechanism of chaos induced by electron-interaction alone? A simple model of a few-electron quantum dot highlights the necessity to go beyond the adiabatic approximation in TDDFT.

9:48AM U13.00004 Time-dependent NEGF calculations of extended systems , ALEXANDER PROCIUK, BARRY DUNIETZ, University of Michigan — A non-equilibrium GF (NEGF) model based on time dependent perturbation theory is developed to propagate electronic structure and molecular conductance of extended electrode-molecule-electrode nanostructures. In this model, we take advantage of the two time variable nature of the KB equations in order to formulate a mixed time-frequency representation for the lesser GF. This allows us to include bulk aﬀected electrodes with non-trivial energy representations in our propagation. It also allows us to express dynamical observables such as current with highly informative Wigner distributions that shed light on the physical causes for certain dynamic features. Preliminary calculations, performed on simple systems, reveal that the dynamic current has both a direct and an alternating contribution. The direct current is due to a bulk aﬀected state and the alternating component is due to a superposition of states. The amplitude of the alternating current can be changed dramatically by adjusting the bias pulse.

10:00AM U13.00005 Many-Body Density Matrix Perturbation Theory , C.J. TYMCZAK, Texas Southern University — One fundamental limitation of quantum chemical methods is the accuracy of the approximate many-body theoretical framework that is utilized. Accurate many- body formalisms for quantum chemical methods do exist, but these methods are computationally very expensive. Methods also exist that are much less computationally expensive such as Hatree-Fock, Density Functional and the Hybrid Functional theories, but at a reduced representation of the exact many-body ground state. This severely limits either the system size that can be addressed accurately, or the accuracy of the representation of the many-body ground state. What is essential is a method which represents the many-body ground state accurately, but with a low computational cost. Recently, a method for determining the response, to any order of the perturbation, within the density matrix formalism has been discovered. This method is very simple and computationally efficient, and it immediately opens up the possibility of computing the variational many- body ground state to unprecedented accuracy within a simplified computational approach. Within this article, we report on the theoretical development of this methodology, which we refer to as Many Body Density Matrix Perturbation Theory. This theory has many significant advantages over existing methods. One, its computational cost is equivalent to Hartree-Fock. Two it is a variational upper bound to the exact energy. And three, it has no self-interaction. 10:12AM U13.00006 Conformational hierarchies of weakly bonded systems: Accuracy of dispersion corrected DFT , ALEXANDRE TKATCHENKO, VOLKER BLUM, MATTHIAS SCHEFFLER, Fritz-Haber-Institut der Max-Planck- Gesellschaft, Berlin, Germany — It is well known that long-range dispersion interactions, important for stabilization of, e.g., molecular crystals, biomolecules and physisorption, are badly described by state-of-the-art xc functionals in DFT, but naturally included in post-HF methods or empirically in force field simulations. 6 We have implemented a semi-empirical C6/R correction [1,2] in the numeric atom-centered orbital based code FHI-aims [3] and obtained correction parameters by fitting to a database of high quality ab initio calculations [2], improving on previous results due to the more accurate basis set (0.5 kcal/mol average error for binding energies using PBE+C6). We assess the accuracy and impact of the correction on conformational energy hierarchies of (i) (H2O)n clusters (n=2-6), (ii) Ala2 and Ala4, and (iii) infinite polyalanine conformers, comparing to published post-HF results for (i) and (ii). Even though the relative energies are not changed for small H2O clusters and Ala2 compared to DFT-GGA, the impact of dispersion on the conformation hierarchy of larger systems is surprisingly large, reaching ∼1-4 kcal/mol for different polyalanine conformers. [1] S. Grimme, J. Comput. Chem. 25, 1463 (2004) [2] P. Jurecka et al., J. Comput. Chem. 28, 555 (2007) [3] V. Blum et al., FHI ab initio molecular simulations (FHI-aims) project.

10:24AM U13.00007 Iterative computation of dielectric eigenmodes , HUGH WILSON, FRANCOIS GYGI, GIULIA GALLI, University of California, Davis — We present an iterative method for the calculation of the eigenvectors of dielectric matrices of materials and nanostructures, based on Density Functional Theory, within a linear response framework. We show that by computing a relatively small number of eigenvectors via iterative dielectric response calculations, one may reconstruct the full dielectric matrix of a given system to high accuracy. The proposed method bypasses the need for the calculation of a large number of excited states required by earlier dielectric matrix computations based on the Random Phase Approximation. The scaling of the algorithm and the eﬃciency of the approach will be demonstrated by the calculation of the static dielectric properties of a variety of nanostructures, including silicon rods and slabs.

10:36AM U13.00008 Comparison of vibrational and electronic contributions to van der Waals interactions , MARK R. PEDERSON, Naval Research Laboratory, KYUNGWHA PARK, Virginia Polytechnic Institute, AMY Y. LIU, Georgetown University — The van der Waals interaction can be caused by either ionic vibrations or instantaneous electronic motion relative to the atomic center. In this study, the vibrational contribution to the van der Waals interaction is formulated by considering the interaction between induced dipoles caused by the infrared-active normal modes of a neutral molecule. Using the derived formula, the contribution is quantiﬁed, within the density-functional theory formalism, using a screened, i.e., self-consistent, vibrational polarizability. Applications for several neutral nonpolar dimers are presented. It is found that the vibrational contributions for the dimers are substantially smaller than their electronic contributions. The ratio of the vibrational to electronic contributions depends strongly on the ratio of the screened vibrational to electronic polarizabilities and on the ratio of the frequency of the strongest infrared-active mode to an ionization energy.

10:48AM U13.00009 Recent progress in ab initio density matrix renormalization group methodology , JOHANNES HACHMANN, JONATHAN J. DORANDO, GARNET KIN-LIC CHAN, Cornell University — We present some recent developments in the ab initio density matrix renormalization group (DMRG) method for quantum chemical problems, in particular our local, quadratic scaling algorithm [1] for low dimensional systems. This method is particularly suited for the description of strong nondynamic correlation, and allows us to compute numerically exact (FCI) correlated energies for large active spaces, up to one order of magnitude larger then can be done by conventional CASCI techniques. Other features of this method are its inherent multireference nature, compactness, variational results, size-consistency and size-extensivity. In addition we will review the problems (predominantly organic electronic materials) on which we applied the ab initio DMRG: 1) metal-insulator transition in hydrogen chains [1] 2) all-trans polyacetylene [1] 3) acenes [2] 4) polydiacetylenes [3]. References [1] Hachmann, Cardoen, Chan, JCP 125 (2006), 144101. [2]

Hachmann, Dorando, Avil´es, Chan, JCP 127 (2007), 134309. [3] unpublished.

Thursday, March 13, 2008 8:00AM - 10:48AM — Session U21 DCP: Surfaces and Interfaces I Morial Convention Center 213

8:00AM U21.00001 Automated Analysis of Nanocar Molecules as Observed by VT-STM. , A. J. OSGOOD, Department of Electrical and Computer Engineering, T. SASAKI, J. M. TOUR, Department of Chemistry, K. F. KELLY, Department of Electrical and Computer Engineering — The observation and measurement of individual nanocar molecules by variable temperature scanning tunneling microscopy (STM) has uncovered a great deal of information regarding their electronic properties and dynamic abilities. While STM is particularly powerful in measuring the properties of individual molecules, it is often desirable and enlightening to obtain information of the ensemble as well. Many groups have previously worked on the automatic detection and recognition of molecules in STM images, however, the complex 4-lobed nature of the nanocar introduces additional challenges. Therefore, we have developed an automated image processing routine that is more robust and able to overcome these problems. We then apply this to the analysis of nanocars imaged by STM at various temperatures and demonstrate the recognition of spinning vs. stationary fullerene wheels on the nanocar molecules by correlating the rotational state with observed changes in their electronic properties.

8:12AM U21.00002 Study of p-diaminobenzene Adsorption on Au(111) by Scanning Tunneling Microscopy , HUI ZHOU, ZONGHAI HU, Columbia University, Department of Physics, DAEJIN EOM, KWANG RIM, LI LIU, GEORGE FLYNN, Columbia University, Department of Chemistry, LATHA VENKATARAMAN, Columbia University, Department of Applied Physics, ALBERTO MORGANTE, Laboratorio TASC-INFM, TONY HEINZ, Columbia University, Department of Physics — From the well-defined conductivity obtained for various individual diamino-substituted molecules spanning two gold contacts, as well as from theoretical analysis [1], researchers have suggested that amines adsorb preferentially to coordinatively unsaturated surface Au atoms through the N lone pair. To understand the nature of the amine binding, we have applied ultrahigh vacuum scanning tunneling microscope (STM) to investigate the adsorption of p-diaminobenzene molecules on the reconstructed Au(111) surface. The STM topography images (taken at 4 K) show that the molecules adsorb preferentially to step edges, corresponding to sites of reduced Au atom coordination. The adsorbed molecules are found to display a distinctive orientation along the step edges. The two-lobe topographic structure of each molecule seen by STM is compatible with the previously calculated charge density of the HOMO level. [1] L. Venkataraman at el., Nano Lett. 7, 502 (2007). 8:24AM U21.00003 Adsorption of colloids with Gaussian-size distribution on clean and pre- patterned substrates , JOAO F. MARQUES, GCEP-Centro de Fisica da Universidade do Minho, 4710 Braga, Portugal, A.B. LIMA, Instituto de Fisica, Universidade Federal da Bahia, Salvador BA, Brasil, NUNO A.M. ARAUJO, GCEP-Centro de Fisica da Universidade do Minho, 4710 Braga, Portugal; T-12 Group, MS B268, Los Alamos National Laboratory, Los Alamos, NM 87545, USA, ANTONIO CADILHE, T-12 Group, MS B268, Los Alamos National Laboratory, Los Alamos, NM 87545, USA; GCEP-Centro de Fisica da Universidade do Minho, 4710 Braga, Portugal — We performed extensive Monte Carlo simulations to study the influence of Gaussian size-distributed colloidal particles on film morphology. Also, we take the limit of irreversible adsorption, which leads to the study of a generalized random sequential adsorption model. We considered size dispersions ranging from 1% up to 20%. The study concerns not only the jammed state but also the full kinetic dependence. Moreover, we also considered the influence of a patterned substrate, consisting of equal sized squares regularly distributed on the surface. Colloids can adsorb solely inside these squares. Results make understandable why colloids with size dispersions up to 4% are considered monodisperse. Finally, we consider in the patterned substrate case cells with a prescribed number of colloids and characterize these deposits.

1 8:36AM U21.00004 Binary mixture study of CF4 and CF3Cl on graphite , PETROS THOMAS, DANIEL VELAZQUEZ, GEORGE HESS, University of Virginia — In a binary mixture adsorption study of CF4 and CF3Cl on graphite from 60 K to 105 K, both the CF3Cl - ν4 and the CF4 - ν3 frequency shifts are measured using IRAS as the spreading pressure (chemical potential) of CF4 is increased. Even though CF3Cl has a much lower saturation vapor pressure (SVP) compared to CF4 (at 80 K, SVP of CF4 is ∼ 70 mT and that of CF3Cl is ∼ 0.1 mT), the CF4 either continuously displaces or adsorbs on top of CF3Cl depending on the initial coverage of CF3Cl on the graphite surface. For temperatures between 70 K and 105 K and lower coverage of CF3Cl, where the molecules lie with their C – Cl axis nearly parallel with the surface, CF4 continuously displaces CF3Cl from the surface. For saturated monolayer coverage of CF3Cl, where the C – Cl axis of the molecules are tilted relative to the surface, the CF4 molecules adsorb on top of the CF3Cl – HOPG template. At 60 K, the displacement of the low-coverage CF3Cl is only partial and the orientation of the remaining CF3Cl is tilted relative to the surface from a nearly ﬂat position.

1Work supported by NSF grant DMR-0305194

8:48AM U21.00005 DFT Estimation of Lateral Interactions in Lattice-gas Models of Br and Cl on Ag(100)1 , T. JUWONO, P.A. RIKVOLD, Florida State University — We studied Br and Cl chemisorbed on a Ag(100) surface, using a latice-gas model and the Density Functional Theory (DFT) method. In this model the Br and Cl ions adsorb at the fourfold hollow sites of the Ag(100) surface, which yields a square lattice of adsorption sites. Five different coverages for each kind of adsorbate were calculated. For each adsorbate and coverage, we obtained the minimum-energy configuration, its energy, and its charge distribution. From these data we calculated dipole moments, lateral interaction energies, and binding energies. Our results showed that for Br the lattice-gas model obtained by fitting to the adsorption energies from the DFT calculation is consistent with long-range dipole-dipole lateral interactions using the dipole moments calculated from DFT charge distribution. For Cl we found less consistency, which indicates that long-range dipole-dipole interactions are not sufficient to describe the Chlorine system.

1Supported by NSF grant number DMR-0240078.

9:00AM U21.00006 Modelling Interfaces in Liquid Crystal/isotropic ﬂuid mixtures , COLIN DEN- NISTON, DAN VRIESINGA, University of Western Ontario — We use all-atom molecular dynamics simulations of mixtures of a real liquid crystal (5CB) and water to study the 5CB/water interface. Properties of the director anchoring at the interface are studied in detail. We map our results onto a continuum model implemented using lattice Boltzmann simulations. We examine anchoring as a function of interface shape and droplet size and discuss the impact on liquid crystal colloidal suspensions.

9:12AM U21.00007 Extended Analysis of a Fluid Configuration Experiment on the Space Shuttle , ERIC BARNETT, MARCUS DEJMEK, Canadian Space Agency — Glass cylinders, partially filled with water, were exposed to the near free-fall environment. In at least two of the cylinders, the liquid-vapour interface adopted a two-interface configuration, as previously predicted. An initial analysis was conducted on 20 images for one cylinder, resulting in contact angles of 6.7±2.7˚ at the upper three-phase line and 26.5±6.2˚ at the lower. Herein, the analysis has been extended to include all 12538 images recorded for each of two cylinders, in addition to correcting for optical distortion. An automated procedure to calculate the contact angles was developed, resulting in values of 2.7±2.8˚ and 16.5±5.3˚ for the same cylinder previously analyzed. The effective gravity (ge) −4 based on this analysis was inferred to be 3.3±2.1 x 10 g/g0, which differs from that previously reported. However, the standard deviation of ge is of the same order of magnitude as the RMS accelerations recorded. The difference in pressures between the two liquid phases was calculated to be 0.21±0.14 Pa. A Fourier analysis was conducted and no significant frequencies could be distinguished.

9:24AM U21.00008 Dissipation at Moving Contact Lines: Effect of Interface Width and Slip1 , MARK ROBBINS, SHENGFENG CHENG, Johns Hopkins University, COLIN DENNISTON, University of Western Ontario — Continuum mechanics predicts a diverging stress and total dissipation when the contact line between a fluid interface and a solid substrate is advanced. Several models for removing this divergence have been advanced. One is that the divergence is cutoff by a finite slip length. Another is that diffusion can remove the singularity for fluid interfaces of finite width. Extensive molecular dynamics simulations of partially miscible binary fluids were used to test these two pictures. The interfacial tension was changed by a factor of 20 and the interfacial width by an order of magnitude. The interface width had no direct effect on the dissipation and diffusion was orthogonal to the predicted direction. The dissipation only depended on system size, the dimensionless capillary number, and the slip length S associated with the flow boundary condition in the fluid far from the contact line. The divergence in stress is cut off at the sum of S and a distance of order the molecular diameter. The dissipation rises rapidly as the amount of slip is decreased. In all cases there is a first order transition where the advancing contact line becomes unstable and a film is entrained.

1Supported in part by NSF DMR-0454947 and CTS-0320907.

9:36AM U21.00009 Counterintuitive connection between layering and mobility in confined fluids , GAURAV GOEL, WILLIAM KREKELBERG, University of Texas at Austin, JEFFREY ERRINGTON, State University of New York at Buffalo, THOMAS TRUSKETT, University of Texas at Austin — Fluids confined to narrow spaces adopt a spatially inhomogeneous distribution of density due to the interactions between the fluid particles and the boundaries. This “density profile” is the most common measure of inhomogeneous structure in confined fluids, but its connection to fluid transport coefficients is poorly understood. We explore via molecular simulations how tuning particle-wall interactions to flatten or enhance the particle layering of a model Weeks-Chandler-Andersen (WCA) confined fluid impacts its self-diffusivity, viscosity, and entropy. Counterintuitively, interactions that eliminate particle layering significantly reduce confined fluid mobility, while those that enhance layering have the opposite effect. Excess entropy helps to both understand and predict these trends. 9:48AM U21.00010 Effective interfacial tension between miscible fluids , JOHN POJMAN, The University of Southern Mississippi, NICK BESSONOV, Institute of Problems of Mechanical Engineering, GLORIA VINER, The University of Southern Mississippi, VITALY VOLPERT, UniversitéLyon I — Isobutyric acid (IBA) and water have an Upper Critical Solution Temperature of 27 C. Using spinning drop tensiometry, we were able to demonstrate the existence of an effective interfacial tension by preparing a drop of isobutyric acid-rich phase below the UCST and then raising the temperature above the UCST. The capillary instability was also observed by rapidly reducing the rotation rate. We also demonstrated that such an effective interfacial tension is not unique to the IBA-water systems but can also occur in the cyclohexane – aniline, which has a Lower Critical Solution Temperature.

10:00AM U21.00011 The Au(111) electrolyte interface: A DFT investigation , TIMO JACOB, SUDHA VENKATACHALAM, Fritz-Haber-Institut der MPG, 14195 Berlin, Germany, FELICE SIMEONE, DIETER KOLB, University of Ulm, 89081 Ulm, Germany — Density functional theory calculations have been performed to derive a detailed model of the electric double layer√ for Au(111)√ in contact with an aqueous H2SO4 electrolyte. At potentials of E ≥ +0.8 V vs. SCE various surface sensitive techniques found evidence for a ( 3 × 7)R19.1◦ (bi)sulfate structure, but the + nature of coadsorbates remains still unclear. Focusing on a sulfate adlayer, the coadsorption of H3O and/or H2O has been studied [1]. The calculated binding + energies show that the coadsorption of a single H3O per sulfate (stabilizing the adlayer by hydrogen bonds) is the most stable configuration. In addition, the charge density distribution within the adlayer well agrees with effective barrier heights deduced from recent distance tunnelling spectroscopy measurements [2]. Afterwards we studied the interfacial structure that forms at negative electrode potentials and found that water arranges near the electrode in an ice-like hexagonal structure with hydronium ions being located in the second water layer and non-specifically adsorbed. Again the calculated charge density distribution shows a perfect correspondence to distance tunnelling spectroscopy measurements. [1] S. Venkatachalam and T. Jacob, Z. Phys. Chem., 221, 1393 (2007). [2] S. Venkatachalam et al., Angew. Chem. Int. Ed., 46, 8903 (2007).

10:12AM U21.00012 NMR Study of Organic Counterion Binding to Perfluorinated Micellar Structures , DOBRIN BOSSEV, Indiana University, MUSTUO MATSUMOTO, MASARU NAKAHARA, Kyoto University — In this study we have applied our previously developed NMR method to study the adsorption of tetramethylammonium (TMA+) and tetraethylammonium (TEA+) counterions to micelles formed by perfluorooctylsulfonate (FOS−) surfactant in water at 30 ˚C. These two counterions induce formation of threadlike surfactant structures that result in well pronounced viscoelastic properties of the solution. To selectively probe the degree of counterion binding we have used 1H and 19F NMR chemical shifts and self-diffusion coefficients that are sensitive to the Stern and diffuse double layers, respectively. The competitive adsorption of TMA+ and TEA+ was examined as a function of the TMA+/TEA+ ratio at a constant FOS− concentration of 100 mM. The two counterions were found to form Stern layer around the FOS− micelles with comparable packing; about one counterion per two micellized FOS molecules. When mixed at intermediate proportions, however, the TEA+ counterion shows preferential binding; the concentration of TEA+ in the Stern layer is found to be twice higher than that of TMA+ at equal total respective concentrations in the solution. These results are discussed in terms of counterion size and hydrophobicity and presented in parallel with those that involved the smaller and more hydrophilic lithium counterion.

10:24AM U21.00013 Design and Fabrication of Micro-textures for Inducing a Superhydropho- bic Behavior on Hydrophilic Materials , DI GAO, LIANGLIANG CAO, ANMIN CAO, HSIN-HUA HU, University of Pittsburgh — Artificial superhydrophobic surfaces are typically fabricated by tuning the surface roughness of intrinsically hydrophobic surfaces. We here report the design and fabrication of micro-textures for inducing a superhydrophobic behavior on intrinsically hydrophilic hydrogen-terminated Si surfaces with an intrinsic water contact angle of about 74 degree. The micro-textures consist of overhang structures with well-defined geometries fabricated by microfabrication technologies, which provide positions to support the liquid and prevent the liquid from entering the indents between the micro-textures. As a result, water is in contact with a composite surface of solid and air, which induces the observed macroscopic superhydrophobic behavior. The principle is applied to fabricate non-aging superhydrophobic surfaces by packing flower-like micrometer-sized hematite particles. The as-fabricated superhydrophobic surfaces do not age even in extremely oxidative environments—they retain the superhydrophobicity after being stored in ambient laboratory air for 4 months, heated to 800 degree C in air for 10 hours, and exposed to ultraviolet ozone for 10 hours.

10:36AM U21.00014 Heterogeneity and Fluctuations in Electrochemical Sensors , JEAN-LUC FRAIKIN, MICHAEL REQUA, MICHAEL STANTON, ANDREW CLELAND, UC Santa Barbara — Metal electrodes submerged in aqueous electrolytes biased with very small voltages frequently display a capacitive low-frequency electrical impedance, which is primarily imaginary but typically displays a 1/f α frequency dependence, with 0.7 ≤ α ≤ 1. This electrode-electrolyte interface is phenomenologically modeled as a constant phase element (CPE). There are a number of explanations for the observed frequency dependence, including geometric arguments based on the assumption of fractal surface geometries, but it is difficult to quantitatively match such models to experiment. We propose a new model to explain this phenomenon, as well as other low frequency electrical characteristics of the electrode-electrolyte interface, using a model that relies on microscopic heterogeneity, allowing for local variations in capacitance and diffusion coefficients. We will present the basic aspects of our model, and describe measurements under way to validate this model, using a combination of impedance measurements and electrochemical noise spectroscopy.

Thursday, March 13, 2008 8:00AM - 10:24AM — Session U26 DCP: Focus Session: Advances in Atmospheric Aerosol Science II Morial Convention Center 218

8:00AM U26.00001 Chemistry of Individual Atmospheric Particles , ALEXANDER LASKIN, PNNL — Aerosols are widely recognized as key elements in atmospheric environment. Chemical and morphological data of individual particles are of crucial importance for understanding of their formation, reactions, atmospheric history and aging. Microprobe analytical techniques have been extensively used in the past to characterize the size, morphology, phase and composition of particles collected in field and laboratory studies. These technique coupled with an appropriate time-resolved aerosol sampling are capable of generating time-resolved single-particle data, which then can be used to follow in detail the time evolution of specific types of aerosols. In this presentation we give a summary of recent research projects carried out in our laboratory that demonstrates how the use of complementary microprobe methods provides new insights into the atmospheric reactions of aerosols, their physical and chemical transformations, and in particular how the obtained data can be utilized to define future directions in laboratory and field studies of aerosols. 8:36AM U26.00002 Heterogeneous oxidation reactions relevant to tropospheric aerosol chemistry studied by sum frequency generation , GRACE STOKES, AVRAM BUCHBINDER, JULIANNE GIBBS-DAVIS, KARL SCHEIDT, FRANZ GEIGER, Northwestern University — Unsaturated organic molecules (terpenes) that commonly form molecular films on tropospheric aerosols can be oxidized by ozone, influencing the microphysics of cloud formation and thus the earth’s climate. Using a laboratory approach that combines organic synthesis with surface spectroscopy, we track the ozone oxidation reactions of tropospherically relevant terpenes bound to glass surfaces that serve as mimics for mineral dust. Specifically, vibrational broadband sum frequency generation (SFG) is used to study a number of tailor-made terpene-modified glass surfaces and to track their interactions with ozone in real time. Exposure of these surfaces to ppm levels of ozone at 1 atm and 300 K yield initial reaction probabilities that are significantly higher than corresponding gas phase reactions. SFG spectra help elucidate the molecular orientations of the surface-bound terpenes and the accessibility of reactive C=C bonds. Our work shows the successful use of SFG spectroscopy to determine heterogeneous atmospheric reaction probabilities and bridges the gap between atmospheric aerosol science and surface spectroscopy.

8:48AM U26.00003 Oxidation of the PAH Coronene by Ozone and OH Radical , ERIN MYSAK, JARED D. SMITH, JOHN T. NEWBERG, KEVIN R. WILSON, HENDRIK BLUHM, Lawrence Berkeley National Laboratory, LAWRENCE BERKELEY NATIONAL LABORATORY TEAM — Reactivity of the polycyclic aromatic hydrocarbon (PAH) coronene to oxidation sources ozone and OH radical is examined. To probe the extent of chemical reaction, product formation, and change in surface morphology as a function of reaction, we examine coronene, adsorbed onto various substrates, from both a surface and bulk perspective, with ambient pressure photoemission spectroscopy (APPES) and aerosol mass spectrometry (AMS), respectively. For bulk on-line analysis, a 20nm thick layer of coronene adsorbed onto NaCl seed particles and reacted with either oxidant in a ﬂow tube showed very little reactant conversion to product in the AMS. However, surface analysis by the APPES of the same reaction where coronene was adsorbed onto model substrates showed up to 50 per cent conversion of the carbon species to oxidized carbon, depending on coronene layer thickness (about 1.5-14A). Data obtained with these complimentary techniques provide evidence for a surface selective reaction.

9:00AM U26.00004 Morphological effects on coated aerosol kinetics , ELIAS ROSEN, EVA GARLAND, TOMAS BAER, University of North Carolina at Chapel Hill — The fate of organic material in the atmosphere can be strongly dependent on the chemical environment under which oxidation takes place. We have investigated the reaction of gas-phase ozone and oleic acid adsorbed to the surface of polystyrene latex spheres and silica aerosols to better understand how the substrate influences heterogeneous kinetics. Flow tube experiments were performed with an Aerosol Time of Flight Mass Spectrometer using a two-laser vaporization/ionization scheme to minimize analyte fragmentation. Pseudo-first-order rate coefficients suggest that ozonolysis of oleic acid proceeds differently on the hydrophobic latex and hydrophilic silica particles. Mechanistic interpretation of these results has been complicated by the discovery that the morphology of oleic acid vapor deposition onto both particle types is non-uniform, which results in the formation of discrete areas of organic material on the particle surface as evidenced by AFM and SEM/EDS measurements.

9:12AM U26.00005 Optical and microphysical properties of organic multicomponent aerosol particles , YINON RUDICH, Weizmann Institute — Atmospheric aerosols affect Earth’s climate in direct and indirect manners. The direct effect of aerosols on climate is by scattering and/or absorbing incoming solar and outgoing terrestrial radiation, which strongly modify Earth’s radiation budget. In addition, aerosols acting as cloud condensation nuclei (CCN) indirectly affect climate and precipitation by modifying the microphysical properties of clouds and cloud coverage. These climatic effects depend on the chemical composition, size and morphology. We will present laboratory studies aiming at understanding how the organic component of atmospheric affect the climate system Specifically, we present the use of cavity ring down (CRD) spectrometer to derive the extinction and complex refractive index of aerosols containing a significant organic component. By precisely measuring extinction as a function of particle size the real and imaginary refractive indices are obtained, and the single scattering albedo may be calculated.. We will present results on aerosol particles containing humic like substances (HULIS). HULIS are a common component of aerosols in the atmosphere. They contribute to the CCN activity, hygroscopic properties and the density of aerosols. In addition, HULIS absorb throughout the visible range, and hence contribute to the direct climatic effect of aerosols. The absorption by organic aerosols is largely unaccounted for in models. Specifically, we will present how the absorption of aerosols containing HULIS and inorganic salts varies with wavelength, test various optical mixing rules and will present results on the extinction of core-shell particles. In addition, we will discuss how the presence of HULIS affects the surface tension of CCN at activation and of cloud droplets and its implications.

9:48AM U26.00006 Oxidation of oleic acid monolayers at air/liquid interfaces , LAURA VOSS, Bowdoin College — Field studies of marine and continental aerosols find that fatty acid films form on aqueous tropospheric aerosols. Oxidation of oleic acid monolayers by ozone was studied to understand the fate of fat-coated aerosols from both fresh and salt water sources. Using vibrational sum frequency generation spectroscopy and reflection absorption infrared spectroscopy, we present a molecular-level investigation of fatty acid monolayers at the air-water and air-sodium chloride solution interface and explore reactions with atmospheric oxidants by these model systems. Coupling sum frequency generation spectroscopy with a Langmuir trough, concurrent spectroscopic and thermodynamic data were collected to obtain a molecular picture of the monolayers. No substantial difference was observed between oxidation of monolayers spread on water and on 0.6 molar sodium chloride solutions. Results indicate that depending on the size of the aerosol and the extent of oxidation, the subsequent oxidation products may not remain at the surface of these films, but instead be dissolved in the aqueous sub-phase of the aerosol particle. Results also indicate that oxidation of oleic acid could produce monolayers containing species that have no oxidized acyl chains.

10:00AM U26.00007 Chemical and Spatial Microscopy of Individual Organic Aerosols , ALEXEI V. TIVANSKI, Department of Chemistry, University of Iowa, REBECCA J. HOPKINS, MARY K. GILLES — Carbonaceous particles originating from biomass burning can account for a large fraction of organic aerosols in a local environment. Presently, their composition, physical, and chemical properties as well as their environmental effects are largely unknown. A distinct type of biomass burn particles, called “tar balls”, have been observed in a number of field campaigns, both in fresh and aged smoke. They are characterized by their spherical morphology, high carbon content and ability to efficiently scatter and absorb light. Here, a combination of scanning transmission x-ray microscopy and near edge x-ray absorption fine structure spectroscopy is used to determine the shape, structure and size-dependent chemical composition of 150 individual tar ball particles ranging in size from 0.15 to 1.2 µm. Oxygen is present primarily as carboxylic carbonyls and oxygen-substituted alkyl functional groups. The observed chemical composition is distinctly different from black carbon and more closely resembles high molecular weight humic-like substances. A detailed examination of the carbonyl intensity as a function of particle size reveals the presence of a thin oxygenated interface layer on the tar balls, indicative of atmospheric processing of biomass burn particles.

10:12AM U26.00008 OH oxidation of organic aerosols. , JARED SMITH, ERIN MYSAK, MUSA AHMED, LBNL, CHRISTOPHER CAPPA, UC, Davis, STEPHEN LEONE, UC, Berkeley and LBNL, KEVIN WILSON, LBNL — Ambient aerosols play a significant role in a variety of atmospheric processes such as direct and indirect effects on radiative forcing. Chemical composition can be an important factor in determining the magnitude of these effects. However, a major fraction of organic aerosols (OA) can not be resolved on a molecular level. Recent identification of high mass oligomeric species as a major component in laboratory and ambient OA has received much attention due to the possibility that these species may account for much of the unknown organic mass in ambient aerosols. Although, a few mechanisms have been proposed, the origin and formation processes of these compounds remain largely unknown. Here we provide strong evidence for a previously unidentified mechanism of extremely rapid oligomer formation, via OH radical initiated oxidation of OA. This process appears capable of converting a sizable fraction of an organic particle to higher mass oligomers within a day of exposure to OH radicals at typical atmospheric concentrations. Furthermore, we have found that rapid volatilization is also important for specific reaction systems, and can lead to the loss of a large fraction of the particle mass. We propose that such a rapid processing is possible due to a radical chain reaction which quickly propagates throughout the entire particle and is only initiated by the surface OH reaction. Thursday, March 13, 2008 11:15AM - 2:15PM — Session V13 DCP DCOMP: Focus Session: Frontiers in Electronic Structure Theory III Morial Convention Center 204 11:15AM V13.00001 Dielectric Properties of Ice and Liquid Water from First Principle Calculations1 , DEYU LU, FRANCOIS GYGI, GIULIA GALLI, UC Davis — We present a first-principle study of the dielectric properties of ice and liquid water. The eigenmodes of the dielectric matrix, −1, are analyzed in terms of maximally localized dielectric functions similar, in their definition, to maximally localized Wannier orbitals obtained from Bloch eigenstates of the electronic Hamiltonian. We show that the lowest eigenmodes of −1 are localized in real space and can be separated into groups related to the screening of lone-pairs, intra-, and inter-molecular bonds, respectively. The local properties of the dielectric matrix can be conveniently exploited to build approximate dielectric matrices for efficient, yet accurate calculations of quasiparticle energies.

1This work was supported by DOE SciDAC grant DE-FC02-06ER25794.

11:27AM V13.00002 Strong hybridization of Frenkel excitons in Mott insulators: a novel Wannier function perspective* , CHI-CHENG LEE, Brookhaven National Laboratory, H. C. HSUEH, Tamkang University, WEI KU, Brookhaven National Laboratory — Linear response scheme of the time-dependent density-functional theory (TDDFT) has been quite successful in the study of the excitations of weakly correlated systems. However, its applicability to strongly correlated systems remains unclear, especially due to the poor quality of the exchange-correlation kernel essential for those systems. On the other hand, the local-density approximation + Hubbard U (LDA+U) approximation has been shown to describe quite successfully the ground-state properties and electronic band structures of Mott insulators. Therefore, it is timely to investigate the linear response of the LDA+U functional in the framework of TDDFT in describing excitations of strongly correlated systems. In this talk, a theoretical (diagrammatic) framework of the linear response of LDA+U (TDLDA+U) functional will be presented and applied to the study of Frenkel excitons in NiO within the ﬁrst-principles Wannier basis. The advantages and disadvantages of LDA+U functional will be discussed, in comparison with more advanced many-body approaches. [1] B. C. Larson, et al. PRL 99, 026401 (2007)*Work supported by U.S. DOE - CMSN

11:39AM V13.00003 Propagation of strongly bound Frenkel excitons in LiF: An effective two- particle kinematic approach of super-atom in ab initio Wannier basis1 , CHEN-LIN YEH, HUNG-CHUNG HSUEH, Department of Physics, Tamkang University,Taiwan, WEI KU, Condensed Matter Physics & Materials Science Department, Brookhaven National Laboratory, NY, USA — A general new first-principles Wannier function based method is proposed to better understand the propagation of strongly bound Frenkel excitions. Specifically, long-standing debate of the Frenkel nature of the excitons in LiF is made apparent by the formation of a “super-atom” consisting of Wannier orbitals from both Li and F. On this basis, a new approach is proposed by formulating the kinematic contribution to the propagation of the exciton via an effective two-particle hopping kernel. The same kernel contains both the mass enhancement at strong binding and the decay into continuum at weak binding, and is thus exact in both limits. This kinematic effect is compared with found to overwhelm the conventional interaction-based propagations of exciton in LiF. This general theoretical framework can be directly applied to the study of propagation of local excitations of strongly correlated systems.

1National Science Council No. 106, HoPing E. Road, Sec.2, Taipei 10622, Taiwan (R.O.C.)

11:51AM V13.00004 Ab-initio Total Energy Calculation for Full-potential Multiple Scattering Theory Methods1 , YANG WANG, Pittsburgh Supercomputing Center, Carnegie Mellon University, AURELIAN RUSANU, MALCOLM STOCKS, DON NICHOLSON, MARKUS EISENBACH, Oak Ridge National Laboratory — The ab initio methods (e.g., KKR, KKR-CPA, LSMS) based on multiple scattering theory have the clear advantage of being able to calculate the Green function in a straightforward manner, which has important implications in the application of electronic structure calculations. But these methods have mostly been implemented within muffin-tin approximations. Recent advances in the numerical implementation of full- potential multiple scattering theory and, in particular, the development of an innovative Poisson equation solver have made carrying out the fully self-consistent full-potential calculation possible. In this presentation, we discuss various implementations of the full-potential total energy calculation, and we investigate the convergence of the total energy with respect to the angular momentum expansion cutoff for scattering matrices. Finally, we compare the full-potential total energy with the muffin-tin approximation results.

1This work is supported by US-DOE, Oﬃce of Basic Energy, Division of Materials Science and Engineering.

12:03PM V13.00005 A quantum chemistry roadmap towards highly accurate adsorption energies at ionic surfaces , BO LI, Fritz-Haber-Institut der Max-Planck-Gesellschaft, ANGELOS MICHAELIDES, London Centre for Nanotechnology, University College London and Fritz-Haber-Institut der Max-Planck-Gesellschaft, MATTHIAS SCHEFFLER, Fritz-Haber-Institut der Max-Planck-Gesellschaft — A roadmap is established to compute adsorption energies of molecules at ionic surfaces with an accuracy approaching chemical accuracy (a precision of 1 kcal/mol or ∼43 meV). The approach relies on established quantum chemistry methodologies and involves a separation of the total adsorption energy into contributions from Hartree-Fock and electron correlation, the use of embedded cluster models of the substrate, and extrapolations to the complete basis set limit. Application of the procedure to the example of water on salt, with electron correlation treated at the CCSD(T) level, yields an adsorption energy for a water monomer on NaCl(001) of 480 ± 20 meV.

12:15PM V13.00006 Surface energies of semiconductors by the energy density method , MIN YU, RICHARD M. MARTIN — Energy Density formalism within the first-principles pseudopotential density functional theory has been proposed by Chetty and Martin1 in 1990s. Although the energy density function is non-unique, nevertheless integrals over surface regions provide unique results for surface energies, and calculations have been carried out by several groups2,3 to study the polar surfaces and interfaces of solid state systems such as GaAs (111) and (1¯1¯1)¯ polar surfaces. In our work, we apply this method to wurtzite CdSe to determine the energy of of various polar surfaces such as (0001), (0001)¯ , and non-polar surfaces such as (1010)¯ , (1120)¯ , from which we can estimate the equilibrium crystal shape for large nanoclusters. 1. N. Chetty and Richard M. Martin, Phys. Rev. B 45, 6074 (1992). 2. K. Rapcewicz, B. Chen, B. Yakobson, and J. Bernholc, Phys. Rev. B 57, 7281 (1998). 3. N. Moll, A. Kley, E. Pehlke, and M. Scheffler, Phys. Rev. B 54, 8844 (1996). 12:27PM V13.00007 Electron-phonon interaction using Wannier functions: from single-layer graphene to cuprate superconductors1 , FELICIANO GIUSTINO, Department of Physics, University of California at Berkeley, and Materials Sciences Division, Lawrence Berkeley National Laboratory — The interaction between electrons and phonons is central to many phenomena, including electrical and thermal transport and superconductivity. Recently the electron-phonon (e-ph) interaction has been the focus of intense research efforts in the physics of high-temperature superconductivity and nanoscale transport. Despite the continued interest in the e-ph problem, first-principles calculations remain challenging due to the large computational effort required to describe e-ph scattering processes in the proximity of the Fermi surface. In this talk I will present a method based on Wannier functions which greatly reduces the computational cost of e-ph calculations [1,2]. The underlying idea is to exploit the spatial localization of electrons and phonons in the maximally localized Wannier representation. After describing the method I will review recent applications to materials of current interest. I will discuss how the e-ph interaction affects the dynamics of Dirac fermions in graphene [3], the origin of superconductivity in boron-doped diamond [1], and the relation between Fermi surface topology and superconductivity in super-hard carbides. I will conclude this presentation by discussing the role of phonons in the angle-resolved photoemission spectra of cuprates [4]. [1] F. Giustino, J.R. Yates, I. Souza, M.L. Cohen, and S.G. Louie, Phys. Rev. Lett. 98, 047005 (2007). [2] F. Giustino, M.L. Cohen, and S.G. Louie, Phys. Rev. B 76, 165108 (2007). [3] C.-H. Park, F. Giustino, M.L. Cohen, and S.G. Louie, Phys. Rev. Lett. 99, 086804 (2007). [4] F. Giustino, M.L. Cohen, and S.G. Louie, http://arXiv:0710.2146.

1Work done in collaboration with J.R. Yates, I. Souza, C.-H. Park, J. Noﬀsinger, M.L. Cohen, and S.G. Louie.

1:03PM V13.00008 Ensemble density functional theory, the atom-in-molecule problem, and reactive charge transfer1 , SUSAN ATLAS, Department of Physics and Astronomy, University of New Mexico, STEVEN VALONE, Materials Science and Technology Division, Los Alamos National Laboratory — A major challenge in large-scale simulations of complex biomolecular and materials systems is the ability to accurately describe reactive dynamics. We have previously described a new multiscale formalism, based on density functional theory and the embedded-atom method, that enables the rigorous encoding of quantum mechanical excitation eﬀects such as charge polarization and charge transfer within a classical potential. Here we describe a new formulation of a key element of the theory: the deconstruction of molecular densities into subsystem atom-in-molecule components via ensemble constrained-search density functional theory. The method is implemented via the self-consistent solution of coupled sets of Kohn-Sham equations in conjunction with chemical potential equalization across subsystems. This leads to a natural interpretation of dynamical charge transfer and charge polarization in terms of an electronic entropy, thus extending the seminal work of Gross, Oliveira, and Kohn (1988).

1Supported by NSF grant CHE-0304710

1:15PM V13.00009 Correction of Finite Size Errors in Many-body Electronic Structure Calculations1 , HENDRA KWEE, SHIWEI ZHANG, HENRY KRAKAUER, College of William and Mary — Finite-size (FS) effects are a major source of error in many-body (MB) electronic structure calculations of extended systems. Reducing FS errors is thus a key to broader applications of MB methods in real materials, and the subject has drawn considerable attention.2 We show that MB FS effects can be effectively included in a modified local density approximation calculation. A parametrization for the FS exchange-correlation functional is obtained. The method is simple and gives post-processing corrections that can be applied to any MB results. Conceptually, it gives a consistent framework for relating FS effects in MB and DFT calculations, which is important if the two methods are to be seamlessly interfaced to bridge length scales. Applications to a model insulator (P2 in a supercell), to semiconducting Si, and to metallic Na show that the method delivers greatly improved FS corrections.3

1Supported by ONR, NSF, and ARO. 2P. R. C. Kent et. al., Phys. Rev. B 59, 1917 (1999); S. Chiesa et. al. Phys. Rev. Lett. 97, 076404 (2006). 3H. Kwee, S. Zhang and H. Krakauer (2007), preprint at http://arxiv.org/abs/0711.0921.

1:27PM V13.00010 Embedding quantum-mechanics in an interatomic potential simulation using local energies , NOAM BERNSTEIN, Naval Research Laboratory, GABOR CSANYI, University of Cambridge — Atomistic simulations that use quantum-mechanical total-energy models provide high accuracy and reliability at the price of computational expense. Classical approximations such as interatomic potentials are much faster, but less transferable. We couple the two approaches concurrently, to describe part of the system quantum-mechanically and part with interatomic potentials, using a weighted sum of atomic energies. This enables us to compute a well defined total energy for the hybrid system with small and controllable errors caused by the boundaries of the QM region. Using tight-binding as a model quantum-mechanical method, we can efficiently evaluate the derivatives of the total energy, including the effects of charge self-consistency, enabling an energy conserving molecular dynamics simulation for a fixed QM region. We show that a localized quantum-mechanical atomic energy can be defined, and that this energy is physically meaningful. We present tests of the method, and discuss convergence with respect to various method parameters, and the effects of moving the QM region during the dynamics.

1:39PM V13.00011 The search for minimum-energy atomic configurations on a lattice: Lamar- ckian twist on Darwinian Evolution1 , MAYEUL D’AVEZAC, ALEX ZUNGER, National Renewable Energy Lab — We examine how two different mechanisms proposed historically for biological evolution compare for the determination of crystal structures from random initial lattice-configurations. The Darwinian theory of evolution contends that the genetic makeup inherited at birth is the one passed on to offsprings. Lamarck surmised additionally that offspring can inherit acquired traits. In the case of lattice-configurations, such improvements consist in A↔B transmutations of atomic sites as guided by “Virtual Atom” energy-gradients(M. d’Avezac and Alex Zunger, J. Phys.: Cond. Matt. 19, 402201 (2007)). This hybrid evolution is shown to provide an efficient solution to a generalized Ising Hamiltonian, illustrated by finding the ground-states of face-centered cubic Au1−xPdx using a cluster- expansion functional fitted to first-principles total-energies. For example, finding all minimum-energy structures of a 32-atom supercell with 95 % confidence requires evaluating 750, 000 configurations using local improvements only, 150, 000 using a reciprocal-space genetic algorithm only, and 14, 000 using the hybrid approach. We consider applying the lamarckian search to further functionals.

1Funded by DOE-SC-BES-DMS. 1:51PM V13.00012 Using genetic algorithms to find from first-principles the minimum-energy crystal structure starting from random cell vectors and random atomic positions.1 , G. TRIMARCHI, M. D’AVEZAC, ALEX ZUNGER, NREL, Golden CO 80401 — We address the global space-group optimization problem in binary metallic AqB1−q alloys using an evolutionary algorithm. A set of crystal structures with randomly-selected lattice vectors and atomic positions is evolved, replacing the highest energy structures with new ones generated through mating or mutation, as well as ab-initio structural relaxation to the nearest local minimum. This was applied to a few compounds whose lattice-type is difficult to guess because the constituent solids A and B have different lattice types (e.g., A is fcc and B is bcc): (i) compounds with the crystal lattice of either A or B constituents, i.e., CdPt3, AlSc3, Al3Sc; (ii) compounds with a crystal lattice different than that of either constituents, i.e., AlSc and CuPd; (iii) compounds whose crystal lattice is not even of a Bravais type, e.g., PdTi3. The optimization scheme retrieved the lowest energy structures within about 100 total-energy evaluations. Not all independent GA sequences end up giving the same final structure; we select the lowest energy structure from all sequences. Using a model calculation, we will discuss how many independent GA sequences are needed to find the lowest energy structure with given confidence.

1Funded by DOE-SC-BES-DMS

2:03PM V13.00013 From grand-canonical density functional theory towards rational compound design , ANATOLE VON LILIENFELD, Sandia National Laboratories — The fundamental challenge of rational compound design, ie the reverse engineering of chemical compounds with predefined specific properties, originates in the high-dimensional combinatorial nature of chemical space. Chemical space is the hyper-space of a given set of molecular observables that is spanned by the grand-canonical variables (particle densities of electrons and nuclei) which define chemical composition. A brief but rigorous description of chemical space within the molecular grand-canonical ensemble multi-component density functional theory framework will be given [1]. Numerical results will be presented for intermolecular energies as a continuous function of alchemical variations within a neutral and isoelectronic 10 proton system, including CH4, NH3,H2O, and HF, interacting with formic acid [2]. Furthermore, engineering the Fermi level through alchemical generation of boron-nitrogen doped mutants of benzene shall be discussed [3]. [1] von Lilienfeld and Tuckerman JCP 125 154104 (2006) [2] von Lilienfeld and Tuckerman JCTC 3 1083 (2007) [3] Marcon et al. JCP 127 064305 (2007)

Thursday, March 13, 2008 11:15AM - 1:03PM — Session V26 DCP: Focus Session: Advances in Atmospheric Aerosol Science III Morial Convention Center 218 11:15AM V26.00001 Measurements of the Chemical Composition of Atmospheric Nanoparticles1 , JIM SMITH, National Center for Atmospheric Research — The Thermal Desorption Chemical Ionization Mass Spectrometer (TD- CIMS) is an instrument that is capable of measuring the chemical composition of particles as small as 4 nm. It accomplishes this with a sensitivity that makes it possible to measure the molecular composition of nanoparticles at ambient concentrations in the atmosphere. For the past ﬁve years, the TDCIMS has been performing measurements of the smallest particles in the atmosphere in order to determine the chemical species and mechanisms responsible for the growth of aerosols formed by nucleation. In this talk I will summarize what we’ve learned from these measurements, which took place in urban areas (Atlanta and Mexico City), a remote location (the boreal forests of Finland), and regions that are combinations of both (Boulder). With the exception of one study in urban Atlanta, in which sulfur species were seen to dominate, most measurements indicate a crucial role played by organic species in the growth of atmospheric nanoparticles. Positive ion TDCIMS measurements in a variety of locations show the presence of methyl and dimethyl amines in particles as small as 8 nm. Other oxidized organics detected in positive ion TDCIMS measurements are presumed to be alcohols, aldehydes, or ketones. Negative ion TDCIMS measurements show the presence of multifunctional organics with carboxylic acid moieties. Laboratory studies using pure and multi-component aerosols are assisting us in identifying the many ions that were observed during our campaigns. Our measurements suggest that reactions of organic acids and organic bases on particle surfaces or within particles may form organic ions and/or salts in particles. Based on these measurements, we hypothesize that the organic salt formation mechanism may be the dominant mechanism by which nanoparticles grow in the atmosphere.

1This research was supported by the Oﬃce of Science (BER), US DOE, grant DE-FG-02-05ER63997 and by NOAA under contract NA05OAR4310101. NCAR is sponsored by NSF.

11:51AM V26.00002 Laboratory-Measured Nucleation Rates of Sulfuric Acid and Water from the SO2 + OH Reaction , DAVID R. BENSON, LI-HAO YOUNG, SHAN-HU LEE, Kent State University — We present results of the laboratory study of sulfuric acid-water binary nucleation system. H2SO4 was produced through the reaction of SO2 + OH → HSO3 in the presence of SO2, OH, O2, and H2O in a fast ﬂow reactor at 288 K and atmospheric pressure. OH was produced from the photolysis of water vapor. The power dependence of nucleation rate 6 9 −3 (J) on sulfuric acid concentration ([H2SO4]) was 2 - 10 in the [H2SO4] range from 3×10 - 1× 10 cm . This power dependence increased with decreasing RH and increasing nucleation time. The power dependence of J on RH was 10 - 15 for the RH values from 10 - 50%. The measured aerosol sizes ranged from 4 - 20 nm. These aerosol sizes were larger for higher [H2SO4], higher RH, and higher nucleation times. The eﬀects of RH on aerosol growth were also more pronounced at higher [H2SO4] and with higher nucleation times.

12:03PM V26.00003 The enhancement of aqueous aerosol formation by ions and radicals , SAMUEL KEASLER, RICKY NELLAS, HYUNMI KIM, Louisiana State University, JOSEPH FRANCISCO, Purdue University, BIN CHEN, Louisiana State University — The formation of aqueous aerosols in the atmosphere is of significant importance due the role of these particles in heterogeneous chemistry. One important mechanism for the formation of these aerosols is the multi-component nucleation of water with other compounds present in the atmosphere, such as ions and radicals. We have applied the AVUS-HR approach developed in our group for to examine the nucleation of water in the presence of both single ions and ion pairs, and to the binary nucleation of water with hydroxyl and peroxyl radicals. This method allows us to efficiently calculate the free energy profile for these nucleation processes as a function of the cluster size and composition. This information can give us a clear picture of the role that these ions and radicals may play in forming aqueous aerosols.

12:15PM V26.00004 Scaled Nucleation in a Lennard-Jones System , BARBARA HALE, TOM MAHLER, University of Missouri-Rolla, JERRY KIEFER, St. Bonaventure University — Scaling of the vapor-to-liquid nucleation rate, J, is examined in a model Lennard- Jones system using Monte Carlo derived rate constant ratios for growth and decay of small clusters. The model assumes a dilute vapor system of non-interacting clusters and the steady-state nucleation rate formalism expressed as a summation over products of rate constant ratios. The nucleation rates so obtained are 3/2 examined in a scaling plot of log J vs. ln S/[Tc/T − 1] [Hale, B. N., J. Chem. Phys. 122, 204509 (2005)], the general form of which has been recently used to test the consistency of nucleation rate data [Gharibeh, M., Kim, Y., Dieregsweiler, U., Wyslouzil, B., Ghosh, D. and Strey, R., J. Chem. Phys. 122, 094523 (2005); Brus, D., Zdimal, V., and Stratmann, F., J. Chem. Phys. 124, 164306 (2006)]. 12:27PM V26.00005 The Nucleation Rate and the Gibbs Free Formation Energy of a Cluster , H.R. KOBRAEI, Murray State University — In this work, we present an atomistic/molecular model along with the classical approximation for the Gibbs free formation of nuclei. The free formation energy of the critical cluster plays an essential role in the calculation of nucleation rates. Thus, we have constructed a nucleation rate relation which is easy to calculate and its result is relatively simple to compare with experimental data. The energy formation of a cluster has a few more terms than the traditional classical model. Furthermore, the extra terms in this approach have their roots in the molecular treatment of a cluster formation and they are temperature dependent. We have compared the result of this approach with the original classical theory along with some experimental data. Our initial results seem promising and the temperature correction has a correct trend.

12:39PM V26.00006 Dynamical investigation of water clusters in atmospheric conditions , FRANCESCA BALETTO, King’s College London, London WC2R 2LS, UK, MAL-SOON LEE, UGUETTE F.T NDONMGOUO, SANDRO SCANDOLO, ICTP, Trieste I-34014, Italy — Addressing environmental challenges via first principle calculations is one of the most promising subjects of numerical simulations. Here, we investigate the dynamical evolution of water clusters, namely the dimer and the hexamer, which are abundant in our atmosphere. We use these two clusters as prototypes to clarify long-standing dilemma of greenhouse effects and ozone depletion. To begin with, I will show the behavior of HCl on water hexamers [1]. Our calculations show that at zero temperature the most energetically favorable structure is obtained when the HCl is completely dissociated. At temperatures T ∼ 200 K, the vibrational entropic effects stabilize the non-dissociated clusters. This behavior is traced back to the large dynamic effects associated with the flexibility of the planar cluster. Water vapor absorption in the far-infrared region accounts a large portion of the total radiative absorption responsible for the greenhouse effect. We found that at T close to 200K, the dimer dynamics is fully anharmonic and the calculated adsorption strength throughout the far-infrared spectra is smaller than the measured vapor absorption continuum [2]. [1] U.F.T. Ndomgouo et al. JPCA accepted [2] M-S. Lee, et al. submitted

12:51PM V26.00007 Modeling the Growth of H2O-D2O Nanodroplets , SOMNATH SINHA, BARBARA E. WYSLOUZIL, The Ohio State University, GERALD WILEMSKI, Missouri University of Science and Technology — Using experimental data for water condensation in supersonic nozzles, including SAXS measurements of position-resolved nanodroplet size distributions [Wyslouzil, et al., Phys. Chem. Chem. Phys. 9, 5353 (2007)], we test five different droplet growth models. Three nonisothermal growth models estimate temperature differences between the droplets and the carrier gas; the two isothermal models do not. In general, we found that none of the growth laws agrees well with the experimental data. Although the droplets should be hotter than the carrier gas for our experimental conditions, our results suggest that the nonisothermal models over predict the average droplet temperatures. This leads us to hypothesize that the average temperature is not a good estimate of the most likely temperature of the growing droplets. To accurately predict growth in the nanodroplet regime, droplet growth models will need to account better for the full distribution of temperatures of growing droplets because the main contribution to growth is likely to come from droplets cooler than the average.

Thursday, March 13, 2008 2:30PM - 5:18PM — Session W26 DCP: Focus Session: Advances in Atmospheric Aerosol Science IV Morial Convention Center 218

2:30PM W26.00001 ”The optics of atmospheric aerosol particles” , CHRISTOPHER SORENSEN, Kansas State University — No abstract available.

3:06PM W26.00002 The Molecular Picture Behind Resonance Phenomena in Aerosol Spectra , RUTH SIGNORELL, University of British Columbia, Chemistry Department — The study of icy aerosol particles with sizes in the submicron range is a highly interdisciplinary subject at the junction of nanosciences, atmospheric physics, and astrophysics. The microphysics of aerosol clouds in the atmospheres of planets and their moons, such as ammonia clouds on Jupiter and Saturn or methane aerosols on Titan, is currently very much in the focus of the scientific community. Particularly broad interest has been sparked by the recent Cassini-Huygens mission to Saturn’s moon Titan, which has illuminated the importance of methane clouds for Titan’s weather and their analogy to the role of water ice clouds in Earth’s atmosphere. The present contribution focuses on the influence of intrinsic particle properties, such as shape, size or architecture, on infrared optical properties of icy aerosol particles. Intrinsic particle properties manifest themselves in mid-infrared extinction spectra by modifying the structure of vibrational bands. We ultimately aim at unravelling the microscopic origin of the characteristic patterns found in the spectra of these weakly bound molecular aggregates. To this end we compare our experimental results with different model calculations combining molecular dynamics simulations with vibrational quantum dynamics.

3:42PM W26.00003 Investigations of Hygroscopic Growth and Phase Transitions of At- mospheric Particles by Noncontact Atomic Force Microscopy (AFM). , BENJAMIN OCKO, Brookhaven National Laboratory, SUSAN OATIS, University of New York, Stony Brook, MATTHEW STRASBERG, STEPHEN SCHWARTZ, ANTONIO CHECCO, Brookhaven National Laboratory — Aerosol particles (nanometer to micrometer sized particles suspended in air) affect atmospheric radiation and cloud microphysics. A correct description of their behavior in the atmosphere is essential to accurate climate modeling. The processes by which initially hydrophobic particles become hygroscopic, accrete water from the vapor, undergo phase transition from solid particles to solution droplets are important but not well understood at a fundamental level. We have carried out AFM studies to measure changes in particle size and morphology as a function of the relative humidity for particles of sodium chloride (a substance whose bulk hygroscopic properties are well characterized) deposited on substrates with differing surface energies (Silicon Oxide, Carboxy- and Methyl-terminated organic thin-films). For particles with height > 50 nm, deliquescence was observed with a relative humidity near 75% (±2%), is consistent with measurements of suspended aerosols. These preliminary results demonstrate that environmental AFM is a viable probe for studying the hygroscopic behavior of salt nanoparticles on solid supports. Supported by the U.S. Department of Energy, DE-AC02-98CH.

3:54PM W26.00004 Extinction by Single and Multiple Particles1 , MATTHEW BERG, CHRISTOPHER SORENSEN, AMIT CHAKRABARTI, Kansas State University — The combined eﬀect of scattering and absorption is referred to as extinction and is responsible for the redistribution of radiant energy by a particle. This presentation will show that extinction is due to wave interference. Simulations of the energy ﬂow caused by the interference graphically demonstrate how extinction redistributes the energy of incident light. Both single and multi-particle systems are considered. A conceptual, phase-based explanation is given that builds on previous work and illustrates the physical meaning of the optical theorem. Implications regarding the measurement of extinction are discussed.

1Funded by the NASA Graduate Student Researchers Program 4:06PM W26.00005 Scattering Patterns for Spherical and Non-spherical Particles , CHRISTOPHER SORENSEN, Kansas State University — Aerosols aﬀect our climate directly by scattering and absorbing light. These optical properties depend on the size, shape, and composition. We have recently described patterns that appear in the phase function for spherical particles, Mie scattering, when the scattered intensity is plotted versus the scattering wave vector q = 2ksin(theta/2) [1, 2]. These patterns involve three diﬀerent power law regimes and a quasi- universality on the phase-shift parameter rho= 2kR(m-1), where R is the radius and m the refractive index. Similar patterns appear for non-spherical particles. These patterns give us an empirical description of scattering by particles of arbitrary shape and refractive index. In other work we have explored the consequences of symmetry or its lack on polarization and backscattering. These results can be useful for predicting the scattering of atmospheric aerosol particles. [1] C.M. Sorensen and D.F. Fischbach, Opt. Commun. 173,145 (2000). [2] M.J. Berg, C.M. Sorensen, and A. Chakrabarti, Applied Optics 44, 7487-7493 (2005). I acknowledge very useful collaborations with M. Berg and A. Chakrabarti.

4:18PM W26.00006 Understanding aerosol-cloud interactions , ATHANASIOS NENES, Schools of Earth & At- mospheric Sciences and Chemical & Biomolecular Engineering, Georgia Institute of Technology — The effects of aerosols on clouds (known as the “aerosol indirect climatic effect”) are thought to have a net climatic cooling effect which partially offsets greenhouse gas warming. Regional impacts of aerosols on precipitation and cloudiness can be even stronger. Despite its importance, the complex and multi-scale nature of aerosol-cloud interactions makes quantitative assessments of the indirect effect one of the most uncertain components of anthropogenic climate change. This talk will present the approaches used to observationally study them and represent them in models. We will provide an assessment of what has been learned and point out key research challenges for the future.

4:54PM W26.00007 Alkyl Polyoxyethylene Surfactant Residue Distribution after Sessile Droplet Evaporation.1 , KWAICHOW CHAN, SCOTT PIERCE, YUNJI MI, Albany State University, HEPING ZHU, USDA Agricultural Research Service, KWAICHOW CHAN COLLABORATION, HEPING ZHU COLLABORATION — Post-evaporation residues of an Alkyl Polyoxyethylene surfactant on a slightly hydrophilic surface are studied. An edge-detecting contrast recognition algorithm is used to measure the areas of small (7-30µm diameter) surfactant “islands” which form during the evaporation process as a result of ﬂows within the droplet and surface tension gathering. “Island” distributions broaden with increased concentration, accompanied by higher mean interior island size. Fitting the histogram of island sizes beginning with the principle peak reveals a general form: y = (6 × 108)Cx−α where y is frequency, C the concentration and α is a constant having value between 2.55 and 3.00. Log-log plots evidence a linear behaviour over two orders of magnitude. Total area covered does not increase in a linear fashion with concentration, as one may expect. Rather, a “critical” concentration is achieved at approximately 0.15%, above which area increase is less pronounced.

1Funding was made possible (in part) by 5P20MD0001085-04 from the National Ctr on Minority Health and Health Disparities. Views expressed are the presenter(s)’, and do not consitute endorsement by DHHS.

5:06PM W26.00008 ABSTRACT WITHDRAWN —

Friday, March 14, 2008 11:15AM - 2:51PM — Session Y7 DBP DCP: Control of Light with Bacteriorhodopsin Morial Convention Center RO5

11:15AM Y7.00001 Earle K. Plyler Prize Talk: Stark Realities , STEVEN BOXER, Stanford University — Stark spectroscopy is the effect of an electric field on a spectrum. Measurements of the Stark effect give information on the change in dipole moment and polarizability for a spectroscopic transition. The great majority of Stark effect measurements have been and still are made in the gas phase where spectroscopic transitions are very narrow and a Stark splitting can be readily measured. There are many fewer examples of Stark spectroscopy measurements in condensed phases, largely because of the perceived difficulty of applying a large electric field. While this is the case for liquid samples, where molecular alignment and low breakdown voltages complicate the measurement, it is simple to immobilize the molecule of interest, either by embedding it in a thin polymer film or by freezing the solvent. The latter is completely general and any sample that forms a high quality optical glass, including protein samples, can be studied. In this talk I will present an overview of applications of Stark effects to diverse systems. We divide the phenomenon into two broad classes: classical Stark effects, where the applied field acts as a perturbation shifting a transition; and non-classical Stark effects, where the applied field affects the intrinsic absorption lineshape and/or populations of states. Classical Stark effects provide quantitative information on the dipolar nature of excited states for electronic or vibrational transitions. Once calibrated, the spectroscopic transition can be used to probe electric fields in organized complex systems such as proteins and changes in those fields accompanying mutations, catalysis, ligand binding and folding. Vibrational Stark effects are particularly useful in this context, and this has led to diverse strategies for introducing unique and sensitive probes for electrostatic fields in proteins. Non-classical Stark effects embrace the many effects that electric fields can have on reaction dynamics, particularly involving electron transfer, either photoinduced or in mixed valence systems. For such systems, the electric field can alter the absorption or emission lineshape substantially because the potential surface depends upon the field and the spectrum depends on the shape of the potential. Examples of each type will be presented.

11:51AM Y7.00002 Protein-Based Three-Dimensional Memories and Associative Processors1 , ROBERT BIRGE, University of Connecticut — The field of bioelectronics has benefited from the fact that nature has often solved problems of a similar nature to those which must be solved to create molecular electronic or photonic devices that operate with efficiency and reliability. Retinal proteins show great promise in bioelectronic devices because they operate with high efficiency (∼0.65%), high cyclicity (>107), operate over an extended wavelength range (360 – 630 nm) and can convert light into changes in voltage, pH, absorption or refractive index. This talk will focus on a retinal protein called bacteriorhodopsin, the proton pump of the organism Halobacterium salinarum. Two memories based on this protein will be described. The first is an optical three-dimensional memory. This memory stores information using volume elements (voxels), and provides as much as a thousand-fold improvement in effective capacity over current technology. A unique branching reaction of a variant of bacteriorhodopsin is used to turn each protein into an optically addressed latched AND gate. Although three working prototypes have been developed, a number of cost/performance and architectural issues must be resolved prior to commercialization. The major issue is that the native protein provides a very inefficient branching reaction. Genetic engineering has improved performance by nearly 500-fold, but a further order of magnitude improvement is needed. Protein-based holographic associative memories will also be discussed. The human brain stores and retrieves information via association, and human intelligence is intimately connected to the nature and enormous capacity of this associative search and retrieval process. To a first order approximation, creativity can be viewed as the association of two seemingly disparate concepts to form a totally new construct. Thus, artificial intelligence requires large scale associative memories. Current computer hardware does not provide an optimal environment for creating artificial intelligence due to the serial nature of random access memories. Software cannot provide a satisfactory work-around that does not introduce unacceptable latency. Holographic associative memories provide a useful approach to large scale associative recall. Bacteriorhodopsin has long been recognized for its outstanding holographic properties, and when utilized in the Paek and Psaltis design, provides a high-speed real-time associative memory with variable thresholding and feedback. What remains is to make an associative memory capable of high-speed association and long-term data storage. The use of directed evolution to create a protein with the necessary unique properties will be discussed.

1Supported by NSF and DARPA. 12:27PM Y7.00003 Optical Fourier and Holographic Techniques for Medical Image Processing with Bacteriorhodopsin , CHANDRA YELLESWARAPU, University of Massachusetts Boston — The biological photochrome bacteriorhodopsin (bR) shows many intrinsic optical and physical properties. The active chromophore in bR is a retinal group which absorbs light and goes through a photocycle. The unique feature of the system is its flexibility – the photocycle can be optically controllable since the process of photoisomerization can go in both directions depending on wavelength, intensity and polarization of the incident light, opening a variety of possibilities for manipulating amplitude, phase, polarization and index of refraction of the incident light. Over the years we studied the basic nonlinear optics and successfully exploited the unique properties for several optical spatial filtering techniques with applications in medical image processing. For nonlinear Fourier filtering, the photo-controlled light modulating characteristics of bR films are exploited. At the Fourier plane, the spatial frequency information carried by a blue probe beam at 442 nm is selectively manipulated in the bR film by changing the position and intensity of a yellow control beam at 568 nm. In transient Fourier holography, photoisomerizative gratings are recorded and reconstructed in bR films. Desired spatial frequencies are obtained by matching the reference beam intensity to that of the particular frequency band in object beam. A novel feature of the technique is the ability to transient display of selected spatial frequencies in the reconstructing process which enables radiologists to study the features of interest in time scale. The results offer useful information to radiologists for early detection of breast cancer. Some of the highlights will be presented.

1:03PM Y7.00004 Light manipulation with Bacteriorhodopsin membrane self-assembled on high-Q photonic structures1 , FRANK VOLLMER, Rowland Institute at Harvard, Harvard University, Cambridge MA 02142 — Resonant photonic structures such as ring resonators and photonic crystal nanocavities interact evanescently with biological material assembled on a reﬂecting interface. Quality (Q-) factors ∼106 and sub-wavelength modal (V-) volumes signiﬁcantly enhance the interaction so that tuning of microcavity resonances by only few molecules is feasible. Since only few constituents are required, the molecular-photonic interface can be fashioned from self-organizing principles that govern interaction of organic and biological polymers. We demonstrate this bottom-up approach with photochromic Bacteriorhodopsin membrane which we self-assemble on various microcavities. The hybrid molecular-photonic architectures exhibit high Q/V-values and are sensitive to photoinduced molecular transitions and other non-linearities which we utilize for demonstrations of all-optical switching, routing and molecular analysis.

1Co-author: Juraj Topolancik, Rowland Institute at Harvard, Harvard University, Cambridge MA 02142.

1:39PM Y7.00005 The Integration of Bacteriorhodopsin Proteins with Semiconductor Het- erostructure Devices , JIAN XU, Department of Engineering Science and Mechanics, Penn State University — Bioelectronics has emerged as one of the most rapidly developing fields among the active frontiers of interdisciplinary research. A major thrust in this field is aimed at the coupling of the technologically-unmatched performance of biological systems, such as neural and sensing functions, with the well developed technology of microelectronics and optoelectronics. To this end we have studied the integration of a suitably engineered protein, bacteriorhodopsin (BR), with semiconductor optoelectronic devices and circuits. Successful integration will potentially lead to ultrasensitive sensors with polarization selectivity and built-in preprocessing capabilities that will be useful for high speed tracking, motion and edge detection, biological detection, and artificial vision systems. In this presentation we will summarize our progresses in this area, which include fundamental studies on the transient dynamics of photo-induced charge shift in BR and the coupling mechanism at protein-semiconductor interface for effective immobilizing and selectively integrating light sensitive proteins with microelectronic devices and circuits, and the device engineering of BR-transistor-integrated optical sensors as well as their applications in phototransceiver circuits. Work done in collaboration with Pallab Bhattacharya, Jonghyun Shin, Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI; Robert R. Birge, Department of Chemistry, University of Connecticut, Storrs, CT 06269; and GyörgyVáró, Institute of Biophysics, Biological Research Center of the Hungarian Academy of Science, H-6701 Szeged, Hungary.

2:15PM Y7.00006 All-Optical Switching in Bacteriorhodopsin Based on Excited-State Ab- sorption , SUKHDEV ROY, Dayalbagh Educational Institute — Switching light with light is of tremendous importance for both fundamental and applied science. The advent of nano-bio-photonics has led to the design, synthesis and characterization of novel biomolecules that exhibit an efficient nonlinear optical response, which can be utilized for designing all-optical biomolecular switches. Bacteriorhodopsin (bR) protein found in the purple membrane of Halobacterium halobium has been the focus of intense research due to its unique properties that can also be tailored by physical, chemical and genetic engineering techniques to suit desired applications. The talk would focus on our recent results on all-optical switching in bR and its mutants, based on excited-state absorption, using the pump-probe technique. We would discuss the all-optical control of various features of the switching characteristics such as switching contrast, switching time, switching pump intensity, switched probe profile and phase, and relative phase-shift. Optimized conditions for all-optical switching that include optimized values of the small-signal absorption coefficient (for cw case), the pump pulse width and concentration for maximum switching contrast (for pulsed case), would be presented. We would discuss the desired optimal spectral and kinetic properties for device applications. We would also discuss the application of all-optical switching to design low power all-optical computing devices, such as, spatial light modulators, logic gates and multiplexers and compare their performance with other natural photoreceptors such as pharaonis phoborhodopsin, proteorhodopsin, photoactive yellow protein and the blue light plant photoreceptor phototropin.