Neutron Vibrational Spectroscopy

A.J. (Timmy) Ramirez-Cuesta Luke L. Daemen Yongqiang Cheng Spallation Neutron Source Oak Ridge National Laboratory

ORNL is managed by UT-Battelle for the US Department of Energy The S(Q,w) Map

w=0 Elastic Scattering Diffraction Structural Information

2 "Let there be light"

3 4 How to measure INS (1)

Direct Geometry Instrumentation 4000

3500

Direct geometry instruments 3000

)

- m

measure Q trajectory is c

( 2500

e f

determined by the angle s

n 2000

and energy transfer. y g

r 1500

e n

Examples: ARCS, CNCS, E HYSPEC, SEQUIOA 1000 500

0 0 10 20 30

Momentum transfer (A-1)

)

(

n e

L t

2 n I Incident neutron beam is 0 10 20 30 40 50 60 70

Energy (meV) s

monochromatic t

o c

determining the incident

u Distance

energy E1. e N That determines T1. We L1 12000 13000 14000 15000 16000 measure the ToF and we ToF (ms) can work out T2. Resolution is almost constant in units of Ei time 5

VISION: a high throughput spectrometer for neutron vibrational spectroscopy

Yongqiang Cheng, Luke Daemen, A.J. (Timmy) Ramirez-Cuesta Spallation Neutron Source, Oak Ridge National Laboratory, Oak Ridge, TN 37931 USA

VISION offers users a variety of sample environments How to measure INS (2) Polybenzene nanothreads synthesized at high pressure: single nanothreads VISION is best thought of as and experimental/computational capabilities: the neutron analogue of a Structural inference through modeling of vibrational spectra Indirect Geometry Instrumentation Raman spectrometer. It is optimized to characterize molecular vibrations in a wide Benzene samples were compressed to 20 GPa at room temperature, 4000 range of crystalline and

maintained at this pressure for one hour, and slowly released to ambient y

3500 t

i disordered materials over a

s pressure at an average rate of 2 GPa /hr to recover a solid white product. L n 2 e t broad energy range (1 meV

3000

) 1

- to >500 meV), while

m c

( 2500

supercomputers and

r simultaneously recording

e f s 0 50 100 150 200 250 300 350 computer clusters with n 2000

a structural changes using

t s

Energy transfer (meV) DFT and past-DFT codes

t y

n 40

g diffraction detectors in the u

r 1500

o c

n 3 mg sample synthesized on SNAP in diamond

E backscattering position and n

1000 o r

t 20 anvil cells and measured on VISION. u at 90°. ortho/para H e 2 500 N ✔ converter 0 Comparison of the experimental data from 0 5000 10000 15000 20000 25000 30000 L1 0 10 20 30 VISION and a series of DFT calculations of -1 ToF (ms) JANIS closed-cycle Momentum transfer (A ) 3 refrigerator (5-600K) hypothetical structures that contain sp carbon and the correct stoichiometry (C:H ratio 1:1) Resolution is almost constant in units of Δω/ω~1.5% allows us to determine which structure Proposed mechanism of polymerization Distance corresponds to the measured spectra. (zipper structure) ✔

Figures on the far left show the superposition of Computer modeling is vital to understand the measured spectrum of polybenzene with the spectra. The calculations shown here time calculated INS spectra of the structures took up to 36 hours using 1024 cores with 3 DOI: 10.10 38/ NMAT4CASTE088 P/Materials Studio Incident neutron beam is white. We (containing sp carbon) shown in the right column: SUPPLEMENTARY INFORMATION ✔ top =graphane, middle = tubular structure (highly fix the energy of the scattered in situ electrochemical impedance symmetric) and bottom = zipper structure. The neutrons using a analyzer and filter spectroscopy (EIS) zipper structure provides the better agreement device. between calculation and experiment. That fixes T2. We measure the ToF and we can work out T1. Gas handling panel for gas dosing, mixing, flow, adsorption 6 (vacuum to 200 bar)

VISION is an inverted geometry instrument that offers enhanced performance by coupling a white beam of incident neutrons with two banks

of seven analyzer modules (double-focusing crystal arrays). This Pressure cells (piston, gas, DAC) arrangement leads to improved signal-to-background ratio, and the overall Collaboration with Malcolm Guthrie, Supplementary FigurJohe 9: Nnan Baothrddeadin forg,m eVd biny cCreycloaspidditi on and intramolecular count rate in the inelastic signal is more than two orders of magnitude reaction. Top: A reaction mechanism that forms a sp3 nanothread from benzene molecules The VISION team is always interested in developing and Original publication on carbon greater than that of similar spectrometers currently available. arranged in the benzenena II crnoysthretal. Benadzenes: m Naolectureules ar eMateria oriented in ls,a sl ipp14ed, s43tack along both adding new sample environment capabilities in collaboration the a and b axes of the benzene II crystal structure. An a axis stacking extracted from this crystal (2014) with users. structure is shown in the leftmost column. A series of [4 +2 ] cycloaddition reactions can form a benzene polymer (second and third columns). Aligned olefin functions are then well oriented for a zipper cascade30 to give a fully sp3 hybridized nanothread (fourth column). The cycloaddition and zipper reactions both have negative activation volumes and would thus be promoted under high pressure. The zipper reaction is very exothermic; the slow decompression employed in our experiments may aid in controlling this reaction. Tight binding relaxation of the [4 +2 ] cycloaddition reaction product spontaneously forms the fully sp3 thread in view of its Crystallization of amorphous calcium carbonate Nitrogen adsorption in ZIF-8 metal-organic framework Order-disorder transition in methylammoconsiderable thermniumodynamic st ableaility. Thids st iodidructure can inteerco nvert to the (3,0) and polymer I structures discussed in the main text by Stone-Wales transformation: all three structures should be considered members of a single structural family, since current scattering data does not provide a firm basis to distinguish between them. Although benzene dimers are prone to • Neutron vibrational spectrum cycloreversion, benzene oligomers several repeat units long can be formed at hundreds of MPa 12 – Simiprlaressu tores IR in theand liqu Ramid statean,31. H butigh p rnoessu sreel solecid-tistonate rulespolymer ization appears to facilitate • Amorphous Calcium Carbonate CH NH librations 10 3 3 MAPbI 3 – MA fvoribrationmation of sm domiuch lonnateger str ucduetures to. B lotargetom: Sitncrucoherentturally relax neutroned nanothr ead formed by this (ACC) plays an important role 8 DFT NH torsion

6 3 Fundamentals scattering cross-section for H

in biomineralization H2O LIBRATIONS 4 1st overtones • Density functional theory 2 NATURE MATERIALS | www.nature.com/ naturematerials 23 0 – Use structural data as input to calculate phonons/vibrations • ACC is also of great interest 60 • Vibrational eigenvectors for CO2 sequestration 50

40 MAPbI • Use as input to calculate neutron spectrum y

t 3

i 30 s

Neutron • Provides vibrational mode assignments n

e 20

t T = 5 K n • Different types/structures of ACC I 10 • I. Milas and Y.Q. Cheng (ORNL) 0 • Measurements of vibrations and phonons are important for with varying amounts of water and 0 500 1000 1500 2000 -1 understanding local order Energy (cm ) – Electron-phonon coupling (charge transport) – Thermal conductivity (heat capacity) • What is the nature of the Comparison of neutron and DFT crystallization phase transition, spectra provides a demanding test which is accompanied by the of accuracy of DFT calculation photovoltaic applications expulsion of water?

• Well defined vibrational modes at T = 5 K • Modes broaden significantly • Simultaneous inelastic and with temperature diffraction measurements on – Increasing Debye-Waller VISION at increasing temperatures factor show progressive water loss • Above the MA order-disorder without crystallization transition at T = 160 K the modes are replaced by • Onset of crystallization quasielastic scattering around 530 K is accompanied by water expulsion, but takes 40 mins to complete.

327 K Endothermic dehydration of hydrous ACC starts at ~100°C, and is followed by a sharp exothermic crystallization (at ~530K) of the Cubic (a = b = c) Tetragonal (a = b c) anhydrous ACC to calcite. Schematic representation of 2ac x 2ac x 2cc the free energy profile for the nonclassical formation of CaCO3 According to the corresponding from ion pairs in solution. Here the two lines for ACC represent ZIF-8 = Zn(mIM) = zinc (methyl imidazole) temperature powder diffraction the bounds of a distribution of 2 2 measurements on VISION/NOMAD, possible curves depending on the bound H2O content (Raiteri P. anhydrous ACC persists up and Gale J.D. J. Am. Chem. Soc. • Structures determined by 2010, 132, 17623. N2 adsorbed in the ZIF-8 framework breaks the synchronicity to 530K before crystallization to calcite. of the methyl torsions in the lattice. This effects translates neutron powder into a change in local structure ("gate opening" effect) diffraction at Spallation

NOMAD data Orthorhombic (a b c) Neutron Source (ORNL)

2ac x 2ac x 2cc

MAPbI3: Two Structural Phase Transitions Collaboration with K.Page, H-W Wang, A. Stack, ORNL Collaboration with Joaquin Silvestre-Albero, Univeristy of Alicante, Spain Collaboration with M. Crawford, DuPont Effect of the Instrument Geometry

k’ Q 2휃

k’

Q 2휃

7 k SNS Instrument Suite

8 analyzers VISION neutron beam

diffraction detectors

inelastic detectors • Vibrational spectroscopy with neutrons • Beam line started commissioning 2 years ago • Multifunctional beam line: simultaneous spectroscopy and diffraction • Dynamic range: 0-1000 meV; resolution: < 1.5% • Diffraction: 1.5 - 30 A-1 • Temperature range: 5-700K • Sample environment: high pressure, electric field, gas loading, ... • Great sensitivity to hydrogen, no selection rules, penetration through matter, ...

9 The VISION instrument

• White incident beam, fixed final energy (indirect geometry) • High flux (~5x107 neutrons/cm2/s) and double-focusing • Broadband (-2 to 1000 meV at 30Hz, 5 to 500 meV at 60 Hz) • Constant dE/E throughout the spectrum (~1.5%) • Elastic line HMFW ~150 μs • Backward and 90° diffraction banks

10 Sample environment

JANIS closed-cycle Pressure cells refrigerator (5-700K) (piston, gas, Gas handling panel for diamond anvil). gas dosing, mixing, flow, adsorption (vacuum to 200 bar) in situ electrochemical impedance ortho/para H spectroscopy (EIS) 2 converter

11 The energy spectra

12 The energy spectra (according to VISION)

VISION

13 Vibrational spectroscopy As a first approximation, a chemical bond between two molecular potential atoms can be thought of as a energy curve spring connecting two masses:

k mA mB

Classical mechanics shows R 0 that this system vibrates with a characteristic frequency:

1 휈 = 푘/휇 2휋

where m is the reduced mass:

1 1 1 = + harmonic approximation 휇 푚퐴 푚퐵

14 Vibrational spectroscopy

Dynamics at the atomic level is determined by quantum mechanics rather than by classical mechanics. The relevant problem here is the quantum harmonic oscillator.

This is still an elementary problem of quantum mechanics. The energy levels of the oscillator are quantized and given by:

1 퐸 = ℎ휈 푛 + 푛 2

(n = 0, 1,2, 3, ....)

but the characteristic frequency, n, is still given by the classical value:

1 휈 = 푘/휇 2휋

15 Vibrational spectroscopy

- A molecule with N atoms is a collection of N masses connected with harmonic springs.

- Classical mechanics tells us that such a systems has 3N degrees of freedom.

- Three of these degrees of freedom correspond to translation of the molecule (position of its center of gravity in space), and three correspond to the orientation of the molecule in space (rotation about the center of gravity). This leaves

3.N - 3 - 3 = 3.N -6

vibrational modes.

- For example H2O (N=3) has 3.3 - 6 = 3 modes of vibration.

16 Vibrational spectroscopy bending Several types of vibrational modes in molecules

stretching

(bond angle changes)

Two quantities define a vibrational mode: (bond distance changes) - frequency torsion - set of atomic displacements

Notice that in a normal mode of vibration all atoms move in phase.

(rotation about bond axis; dihedral angle changes) 17 Vibrational spectroscopy Molecular vibrations are useful to chemists because:

- they depend on molecular structure and interatomic or intermolecular forces (chemical bonding)

- specific bonds and functional groups are easily identified (analytical tool)

18 Vibrational spectroscopy How do we observe vibrational modes experimentally ? Crystallographers use diffraction of some form of radiation (light, electron, x-ray, neutron,...) to obtain information on the periodic arrangement of atoms in space. The wavelength of the radiation is comparable to interatomic distances.

Spectroscopists use (inelastic) scattering of radiation (light, x-ray, neutron,...) to excite vibrational modes. The energy of the radiation is comparable to the energy associated with the vibrational excitations.

incident scattered Ei E neutron f neutron

ħw = Ei - Ef (conservation of energy)

Upon interacting with a vibrational mode, the incident neutron loses

energy (from Ei to Ef). The difference in kinetic energy is used to create a vibrational quantum.

19 Momentum is also exchanged ! Vibrational spectroscopy

As long as we have a way to determine Ei and Ef and the number of particles with energy Ei and Ef, we can determine the number of excitations (vibrational modes) created with an energy of ħw = Ei-Ef. The result is the vibrational spectrum:

incident scattered n1 Ei E neutron f neutron

ħw= Ei - Ef

20 Vibrational spectroscopy

VISION (INS) Raman/Infrared Measures dynamics of nuclei (direct) Measures response of electrons (indirect) No selection rules Selection rules apply Great sensitivity to H Cannot always see H High penetration (bulk probe) Low penetration (surface probe) Easy access to low energy range Low energy cutoff applies (on the order of (librational and translational modes) 100 cm-1) Q trajectories in the (ω,Q) map; Gamma point only averaging over the Brillouin zone Weighted by neutron scattering cross Weighted by change in polarizability or section dipole moment Easy to simulate/calculate Difficult to simulate/calculate No energy deposition in sample Heating, photochemistry, ...

21 Vibrational spectroscopy

22 High throughput: INS in minutes

With 14 inelastic banks and 16 diffraction banks, VISION has the highest data rate (up to millions of events per second) among all neutron beam lines in the world. • INS database • Parametric studies • INS study of kinetics

23 High sensitivity: milligrams of samples

Very small amount of CO2 (2.5 mg). In situ observation of surface reactions. Surface science, catalysis, gas capture and storage.

24 High sensitivity: milligrams of samples

• Largest single crystal diamond for DAC • One of the smallest samples for INS • Challenges in sample/beam alignment and background subtraction

25 Conformation: aldopentoses

The vibrational spectrum is sensitive to differences in molecular conformations

Xylose

26 Model validation: Polybenzene nanothreads synthesized at high pressure

Benzene samples were compressed to 20 GPa at room temperature, maintained at this pressure for one hour, and slowly released to ambient pressure at an average rate of 2 GPa /hr to recover a solid white product. DOI: 10.10 38/ NMAT4088 SUPPLEMENTARY INFORMATION

Collaboration with Malcolm Guthrie, John Badding, Vin Crespi Original publication on carbon nanothreads:Nature Materials, 14, 43 (2014)

Supplementary Figure 9: Nanothread formed by cycloaddition and intramolecular reaction. Top: A reaction mechanism that forms a sp3 nanothread from benzene molecules arranged in the benzene II crystal. Benzene molecules are oriented in a slipped stack along both the a and b axes of the benzene II crystal structure. An a axis stacking extracted from this crystal structure is shown in the leftmost column. A series of [4 +2 ] cycloaddition reactions can form a benzene polymer (second and third columns). Aligned olefin functions are then well oriented for a zipper cascade30 to give a fully sp3 hybridized nanothread (fourth column). The cycloaddition and zipper reactions both have negative activation volumes and would thus be promoted under high pressure. The zipper reaction is very exothermic; the slow decompression employed in our experiments may aid in controlling this reaction. Tight binding relaxation of the [4 +2 ] cycloaddition reaction product spontaneously forms the fully sp3 thread in view of its considerable thermodynamic stability. This structure can interconvert to the (3,0) and polymer I structures discussed in the main text by Stone-Wales transformation: all three structures should be considered members of a single structural family, since current scattering data does not provide a firm basis to distinguish between them. Although benzene dimers are prone to cycloreversion, benzene oligomers several repeat units long can be formed at hundreds of MPa pressures in the liquid state31. High pressure solid-state polymerization appears to facilitate formation of much longer structures. Bottom: Structurally relaxed nanothread formed by this

NATURE MATERIALS | www.nature.com/ naturematerials 23 Polybenzene nanothreads

The Raman spectrum is not particularly informative

28 Polybenzene nanothreads • 3 mg sample synthesized on SNAP in diamond anvil cells and ✗ measured on VISION. • Comparison of the experimental data from VISION and a series of DFT calculations of hypothetical structures that contain sp3 carbon and the correct stoichiometry (C:H ratio 1:1) allows us to determine which structure ✗ corresponds to the measured spectra.

- top =graphane, - middle = tubular structure - bottom = zipper

✔ The zipper structure provides the better agreement between calculation and experiment.

29 Diffraction at VISION Simultaneous diffraction and inelastic neutron scattering 3D printed collimators have been tested for VISION to be used in the backscattering diffraction bank.

The reduction of the spurious peaks from the sample is very much noticeable.

Data collected in histogram or event mode

Before

(422) (311) (220) After (331)

(400) Diamond powder (111)

30 VISION pioneered the use of 3D printed collimators

31 VISION: Inelastic, Diffraction and QENS

• Chemistry Oriented INS spectrometer • White incident beam, fixed final energy (indirect geometry) • High flux (~5x107 neutrons/cm2/s) and double-focusing • Broadband (-2 to 1000 meV at 30Hz, 5 to 500 meV at 60 Hz) • Constant △E/E throughout the spectrum (~1.5%) • Elastic line HMFW ~120 μeV • Backward and 90° diffraction banks • 4000 x its predecessor

a) b)

)

(

n I

0 2 4 6 10 15 20 25

32 0 50 100 150 200 250 Energy Transfer (meV) Structure and dynamics of liquids and solutions

- CD3CN-CCl4 (deep) eutectic system

spectroscopy - TE = 210 K; x(CD3CN) at eutectic composition is 0.75

- no hydrogen bonding, but highly

non-ideal system with DHexcess = - 800 J/mol)

- eutectic structure differs when liquid is cooled quickly or slowly from room temperature

diffraction - simultaneous diffraction/spectroscopy is invaluable Analysis of results Spectroscopy provides a wealth of information, but this comes at the price of complex data sets, particularly in large systems.

How do we interpret the results?

Z. Lu et al. "Modulating Supramolecular Binding of Carbon Dioxide in a Redox- 34 Active Porous Host“ under review at Nature Communications Inelastic Neutron Scattering

• Simultaneous transfer of energy and momentum by the same neutron • Transitions are proportional to the amplitude of motion and the cross section of the nuclei. • Simple interaction: 푉 = 휎. 훿(푟 − 푅) • For incoherent inelastic neutron scattering, the spectral intensity is given by:

n n 2  2  • n Q. u Q 1  n  S Q,w   y  l  exp Q. u Q  n l l   l  n!  3  n   휔n

Frequencies and displacements can be calculated from a known structure (DFT, MD, molecular mechanics, etc). With this information S(Q,w) can be calculated for comparison with inelastic neutron scattering data.

More difficult to do for Raman (e--photon interaction) 35 Integrated modeling for data interpretation

Today this is what we do at VISION using VirtuES (Virtual Experiments in Spectroscopy) High throughout

CASTEP VASP Vibrational modes INS simulation Simulated INS Quantum and frequencies (aClimax) spectra Espresso Gaussian Measured INS Data reduction and spectra Sample VISION analysis (Mantid) Measured diffraction

Structure- dynamics Understanding mechanisms and properties at atomic level correlation Peak assignment Mapping out the local potential energy profile using finite (An)harmonicity displacement, frozen phonon, molecular dynamics

Phase transition Revealing the kinetics and the transition pathway 36 Comparison

sample is hexamethybenzene

37 Gate-opening in a metal-organic framework

Structure of blank ZIF-8

and ZIF-8 loaded with N2. The rotation of the methyl groups and the swinging of the imidazolate rings associated with the gate opening can be seen by comparing the marked areas

For clarity the N2 molecules are not shown.

38 Gate-opening in a metal-organic framework

Measured (upper panel) and simulated (lower panel) INS spectra of blank ZIF-8 and

ZIF-8+N2.

The strong peaks are mainly due to vibrational modes involving large displacement of hydrogen (in the methyl groups and the imidazolate rings)

Casco, M. E. et al. Gate-opening effect in ZIF-8: the first experimental proof using inelastic neutron scattering. Chemical Communications, v. 52, n. 18, p. 3639-3642, 2016 39 INS signature of CO2 capture

This study combining NPD, INS and modelling has unambiguously

determined the CO2 binding sites and structural dynamics for MFM-300(VIII) and MFM- 300(VI) . It is confirmed that the proton on the hydroxy group can not only attract and localise

adsorbed CO2 molecules via direct formation of hydrogen bonds, but also affects the macroscopic packing and arrangement

of CO2 molecules in the extended channel.

Z. Lu et al. "Modulating Supramolecular Binding of Carbon Dioxide in a Redox- 40 Active Porous Host“ under review at Nature Communications Studying H2 adsorption in Porous Materials & Surfaces with INS

Probing the interactions of molecules with the host material Characterization of the interaction strength

01 August 2018 41 The Theory

•H2 ground state (J=0) parahydrogen (p-H2) antisymmetric nuclear spin wavefunction () and symmetric rotational wavefunction.

•The first rotational state, (J=1) orthohydrogen (o-H2) symmetric nuclear spin wavefunction () and antisymmetric rotational wavefunction.

• Transitions p-H2  o-H2 are detected with neutrons because neutrons exchange spin states with the H2 molecule.

In solid dihydrogen, H2 molecules rotate equally freely about all three axes and have the rotational constant B with the same value that in gas phase (B=59.6 cm-1). Its energy levels are:

EJ  J J 1 B

The minimum separation between energy levels is DE  2B 01 August 2018 42 The Interactions

-1 •A hydrogen compound that has a value of B=29.3 cm , H3 would do the trick, D2 also works. •A hindered H2 rotor constrained to move in two dimensions.

The potential that governs the motion of a H2 molecule on a surface may be expressed as

2 2 z V ,, z  Kz  z   sin  a  bcos 0 0  • a>0 the molecule is aligned to an axis (1D case). • a<0 the molecule is constrained in a plane (2D case) • The splitting between levels is 1B if a is large and negative, because the energy levels are:

2 01 August 2018 E2D  J B 43 The Energy Levels

12 b=0.2B b=0B 11 10 9 m=0 m=±2 8 7 m=±1 J=2 m=0

6 m=±1

5 m=±2

Energy/B m=0 4 m=±1 3 J=1 2 1 m=±1 1.67 B 2.85 B 2.67 B 0.98 B m=0 0 1.79 B -10 -8 -6 -4 -2 0 2 4 6 8 10 2D a/B 1D

01 August 2018 44 What are we expecting?

01 August 2018 45 Interaction of graphite with Hydrogen

01 August 2018 46 Interaction of graphite with Hydrogen

01 August 2018 47 Interaction of SWNT with Hydrogen

01 August 2018 48 Interaction of SWNT with Hydrogen

01 August 2018 49 Interaction of SWNT with Hydrogen

01 August 2018 50 Interaction of SWNT with Hydrogen

Rotational line splits Molecule aligns in one direction Probably along the grooves between the SWNT

01 August 2018 51 Example #1 H2 in Cu-MOF

Franck Millange, Sam Callear, Richard Walton, Timmy Ramirez-Cuesta Chemical Physics 427 (2013) 9 doi:http://dx.doi.org/10.1016/j.chemphys.2013.07.020.

52 01 August 2018 H2 in Cu-MOF #1

Neutron Energy Loss/meV 0 5 10 15 20 25 30 35

BackScattering 800 ml p-H (4 H2/Cu) 2 BackScattering 600 ml p-H (3 H2/Cu) 2 BackScattering 400 ml p-H (2 H2/Cu) 2 BackScattering 300 ml p-H (1.5 H2/Cu) 2 BackScattering 200 ml p-H (1.0 H2/Cu) 2 BackScattering 100 ml p-H (0.5 H2/Cu)

)

S(Q,

1 4 2 3 1

53 01 August 2018 H2 in Cu-MOF #1

3 Peak 9.0 meV Peak 10.2 meV Peak 12.5 meV Peak 14.5 meV

1 Integrated Area Integrated

0 0 1 2 3 4

Coverage/H :Cu 2

54 01 August 2018 Quantum Sieving Hydrogen in a MOF Difference spectrum

Site #2 After heating H2+D2

)

(

i s

n Site #1

e t

n D

I 2

0 5 10 15 Site #2

0Site #1 20 40 60 80 100 120 140 Quantum sieving is a technique for isotope Energy transfer (meV) separations; heavier isotopes induce favorable adsorption in nanoscale pores due to the difference H dosing + D further dosing in zero point energy of isotopes. 2 2

H A dftoesr ihnega +ti nDg tfou r2th2e0r Kdosing )

) 2 2 .

Site #2 . U

H D U .

2 2 .

(

Site #1 y

n I H2 I 0 5 10 15 20 25 H2 D2

D2 0 20 40 60 80 100 120 140 Energy transfer (meV) Hydrogen is dosed first, so it mostly takes the lower energy site (Site #1), afterwards deuterium Black trace is hydrogen dosed at 77K and cooled down, further deuterium is added at gas is added and has to go to the available site 77K. Red trace is spectrum after warming sample to 220K and cool down. The (Site #2) hydrogen in site #1 has been displaced to site #2

55 Collaboration with Ingrid Weinrauch and Michael Hirscher, Max Planck Institute for Intelligent Systems, Germany Molecular hydrogen solid

56 Molecular hydrogen in porous carbon

57 Molecular hydrogen in porous carbon

Presence of elastic line at 77K is indication of highly dense molecular hydrogen in the pores. The broadening of the elastic line is a consequence of the enhanced mobility of the molecules as the amount of hydrogen increases in the system. Larger pores, where hydrogen is less constrained have more mobility. In the gas the signal is extremely broad.

Presence of the rotor line at 77K is indication of completely immobile molecular hydrogen in the pores. In the case of pure para-hydrogen (previous figure) the line disappears when the hydrogen melts. There is very little broadening of the rotor line, since the momentum transfer is larger that the corresponding one at the elastic line (dynamical trajectory of indirect geometry). The load keeps increasing even at 40 bar.

58 Molecular hydrogen in porous carbon

1. The total integral of the spectral intensity is proportional to the amount of hydrogen in the system (left plot)

2. The integrated area under the elastic peak is proportional to the amount of hydrogen that is in a liquid like and solid like phase (right panel)

3. The integrated area under the rotor line is proportional to the amount of hydrogen in solid like phase (right panel)

59 Summary What is VISION • It is the world’s first high throughput inelastic neutron scattering instrument. • Its overall count rate in the inelastic signal is three orders of magnitude greater than that of similar spectrometers currently available. • It measures vibrational spectra in a broad energy range (1 meV to >500 meV) • It records structural information using diffraction detectors in the backscattering position simultaneously with inelastic neutron scattering • It has integrated modeling capability that helps to interpret the INS spectra

What can be studied with VISION • Hydrogenous and non-hydrogenous materials • Molecular vibration and phonon density of states • Crystalline and disorder materials (powders) • Nano materials • Porous materials • Surface (e.g., catalysis)

Capabilities • In situ gas handling • High pressure: gas cells, clamps cells, DAC • Automatic sample changer

60 • Computer cluster for modeling and data analysis 61 Intermolecular interactions: Deep Eutectic Solvents

+ Most chemistry takes place in solution of pure or mixed solvents

+ We have no predictive, quantitative, microscopic theory of solubility

+ Deep Eutectic Solvents (DES) are now very popular within the field of "Green Chemistry"

+ Our knowledge of the structure of liquids and solutions has improved over the past few decades. Our understanding of intermolecular forces between solvent(s) and solute(s) remains limited. Optical spectroscopy is of limited use, particularly in hydrogen-bonded systems.

+ The study of liquids and solutions has been historically problematic for inelastic neutron scattering because of the effect of Debye-Waller broadening (which requires low T and/or low Q) and recoil on the vibrational spectrum (which requires low Q)

+ New approach to liquids and solutions and new, vast area of research for chemical spectroscopy with neutrons !

62 Structure and dynamics of liquids and solutions

What we can do today on VISION ... simultaneous spectroscopy and diffraction

spectroscopy

- model deep-eutectic system, acetonitrile-chloroform

- TE = 182 K; x(CD3CN) = 0.4 at liquid eutectic composition - strongly non-ideal system because diffraction of hydrogen bonding (DHexcess = 800 J/mol) What is the structure of the (CH CN) :(CHCl ) 3 2 3 3 no model ! molecular complex at the eutectic composition?

63 Instruments Spectrometer configurations

monochromatic beam:

white beam energy = Ei

Ei sample moderator monochromator (e.g., chopper,

Direct geometry crystal, filter,...) ħw = Ei - Ef detector fixed (by monochromator) measured Inverted geometry

white beam E f

ħw = E - E moderator i f sample

Ei Ef measured fixed (by monochromator) detector

64 ħw = Ei - Ef