DOCSLIB.ORG

Signature Redacted Signature of the Author - Mark N

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Signature Redacted Signature of the Author - Mark N PHOTOPHYSICS OF INFRARED MULTIPHOTON ABSORPTION BY THIOPHOSGENE by MARK NELSON SPENCER B.A., University of Pennsylvania (1978) SUBMITTED TO THE DEPARTMENT OF CHEMISTRY IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY at the MASSACHUSETTS INSTITUTE OF TECHNOLOGY DECEMBER 1982 c Massachusetts Institute of Technology Signature redacted Signature of the Author - Mark N. Spencer Signature redacted Department of Chemistry Certified by Jeffrey I. Steinfeld Thesis Supervisor Signature redacted Accepted by Glenn A. Berchtold Chairman, Depa rtmental Committee ArchJWjg MASSACFWCTTS INSTITUR OF CNOLO9y MAR 3 1 1983 LIBRARIES This doctoral thesis has been examined by a Committee of the Department of Chemistry as follows: redacted Professor Robert J. Silbey ,Signature Chairman Professor Jeffrey I. Steinfeld __ ___ __ __ ___ __ __ Signature redactedF-Thesis Supervisor Signature redacted Professor Robert W. Field, 2 PHOTOPHYSICS OF INFRARED MULTIPHOTON ABSORPTION BY THIOPHOSGENE by MARK NELSON SPENCER Submitted to the Department of Chemistry on December , 1982 in partial fulfillment of the requirements for the Degree of Doctor of Philosophy in Chemistry ABSTRACT Infrared-visible double resonance experiments were done on thiophosgene under collisionless conditions and in a bulb to determine the dynamics of infrared multiphoton absorption in its sparse density of states region. In the absence of collisions thiophosgene absorbs at all excitation frequencies. Measurements of the ground state depletion as a function of C0 2 laser frequency do not correlate at all with the conventional infrared absorption spectrum. At excitation frequencies coincident with the v 4 overtone, no population build-up is observed in excited states of the 2v 4 manifold. The depletion of the ground state induced by the C0 2 laser decreases rapidly as the pressure of thiophosgene increases beyond 2 mTorr. Mixed gas experiments show that this collisional effect is proportional to long range intermolecular forces. Computer solution of the density matrix equations for the infrared excitation of prototypical five level vibrational ladders were carried out in conjunction with the experiments. They demonstrate that the observed phenomena are consistent with a model in which a system of extremely weak combination bands lying between 940 and 1100 cm- 1 provide an absorption continuum for C0 2 laser radiation in this frequency region. The computer simulations also allow us to hypothesize that the observed collisional effect is due to pressure broadening of rovibrational transitions in these very weak combination bands. However, the unusually high efficiency with which pressure broadening must occur in order to make this explanation work leaves open the possibility that other mechanisms are responsible for this behavior. Thesis Supervisor: Dr. Jeffrey I. Steinfeld Title: Professor of Chemistry 3 TABLE OF CONTENTS ABSTRACT ... .. ... .. & 0 0 0 0 0 0 . 0 0 S 0 . 0 3 ACKNOWLEDGEMENTS . ... ...... 7 I. INTRODUCTION .. .. ... a a . 4 II. INFRARED -VISIBLE DOUBLE RESONANCE EXPERIME NTS .. a .. a 25 Ammonia . .... 0 a 0 0 0 0 0a . ..... 29 Osmium Tetroxide . ..... 32 ........ .a Biacetyl. .. ... a .. 32 ........ Formaldehyde . .... .. 34 Propynal. ... .....a . ... a .. 37 III. THIOPHOSGENE . .... ..... 41 A. Ground State (X A1 ). .* .. .. .. 42 B. Electronically Excited States . ..... 49 First Excited Singlet States (A(1A2) 49 Second Excited Singlet (B(lA1 )) 53 3 Triplet State (a( A2 )) . a - .. .. .54 IV. THEORY. ....... ....... .. a a 56 A. Schr6dinger Formulation . ... .... 56 Two-Photon Absorption .. a . 60 B. Density Matrix Formulation . a . ...... 67 .aa82 C. Density Matrix Solution: Computer Model . a a a a a a a a 4 . 95 V. EXPERIMENTAL . .. .. a-- * -- a -- -- - a A. Materials .. 95 1. Thiophosgene . 95 2. Added Gases .. 96 B. Delivery System . 96 1. Effusive Beam .. 96 2. Supersonic Beam. 97 3. Bul b Experiments . 98 C. Molecular Beam Machine. 98 . 0 0 .. 0 . 0 . 0 0 0 0 0 0 0 - -- 0 - 0 .106 D. C0 2 Laser E. Dye Laser .. .. .0 . .0 . .* * * 0 -.. .. .. .109 0* . -111 F. Detection System . 0 . G. Triggering System ...... .. .115 .... .118 VI. Res ults . A. Collisonless Experiments . .. 0 0 *.. 118 1. Ground (Vibrationless State). .. .118 0 0. .143 2. Excited States . 0 0 0 B. Static Gas Experiments . 0. .. 146 1. Vibrationless Ground State . .. 146 2. Excited Vibrational States . 165 5 VII. DISCUSSION. .... ...... ... ... * .. * . 188 A. Collisionless Experiments ....... ........ 188 B. Bulb Experiments ... ... ... ... ... 195 REFDNCrS 228 Appendix A. Measurement of Branching Ratios for the 20 130 142n' Progression . ... .... ... .... .. 230 Appendix B. Listing of Program Density Matrix Computer Solution Program . ...... ....... ...... 245 Appendix C. Reprint of "Influence of collisions on coherent IR multiphoton absorption in thiophosgene" . ... 253 Appendix D. Reprint of "Photophysics of infrared multiphoton excitation in thiophosgene . ... ... 256 6 Acknowl edgements My first thanks go to my advisor, Jeff Steinfeld, who decided that I would be less of a menace to MIT by doing my experimental work at Brookhaven. Doug Brenner deserves special acknowledgement: He drilled in me the importance of not making mistakes---three diffusion pumps later, I believe I have finally achieved perfection. If the southern California sun doesn't mellow Doug out I suggest phenobarbitol. To the other members of my committee: Robert W. Field once told me that, contrary to popular belief, he would be impressed with a solid piece of spectroscopic work done on a molecule having more than two atoms--Sorry, Bob. I recommend that Professor Field attempt to break the Soviet endurance record for orbiting the earth in a space station. Bob Silbey deserves much credit for my development as a scientist. Perhaps after reading this thesis, he will relieve himself of his duties on the admissions committee. I must express my gratitude to certain senior members of the Steinfeld group: My eternal thanks to Chris Reiser for his electronics expertise, for his computer know-how and for his careless leaving behind of 5.76 problem sets. To Craig Jensen for leaving me a drug store when he left me his desk. And to Melissa Charron for showing us all how to be child-like without being childish. Maybe this Christmas Santa will bring her a puppy. Of my peers: Since I've known Joseph Salvadore Francisco I can honestly say that some of my best friends are black. Techniques that Joe taught me at MIT will prove to be indispensable at Columbia and throughout my entire life. He even knows a little science. I wish Dave 7 Harradine much financial success in his future; sex change operations are very expensive. Eric Schweitzer is one person I believe who would benefit immensely from hallucinogenic drugs. Bobbi Roop will always be remembered for her fascinating group seminars. Perhaps a quaalude in her beer would help her delivery. Since I've met Leo Laux, I've learned that you can't judge a person by his name. (Could his middle name be Bagelan?) Unabashed thanks goes to Neil Shinn, Dave Reisner, Precila Ip, Daisy Chawla, Amit Sinha, Dan Imre, Don Kormos, Pierre Tutundjian, James Mack, and any other nationality I have left out. Most of the ideas expressed in the discussion are the result of long and fruitful discussions with Hal Galbraith and Jay Ackerhalt of Los Alamos National Laboratory and I owe them an eternal debt. - When not doing theory, Hal is tinkering in his woodworking shop. I suspect that when this thesis is published, he will be tinkering full time. Thanks also go to the theoretical team of Goodman, Stone and Thiele for their unique insights. Where else, but in southern California, can one find a biologist, a chemist trained by John Ross and an anarchist doing theory together? I am especially in debt - spiritually and financially - to Vera Spanos for typing this manuscript and for putting up with my many missed deadlines. Any mistakes you find in this thesis are Vera's fault - not mine. None of the experiments described in this thesis could have been done without the work of the support staffs of Brookhaven and MIT. Their contribution to my research has been immeasurable and they must, therefore, share the blame for it. 8 Thanks to Ken Lew and Tom Fox of Children's Hopsital Medical Center who gave me the best career opportunity of my life when they offered to write a recommendation for me to medical school. And, lastly, special thanks to my parents who wisely persuaded me not to become a bricklayer. 9 I. INTRODUCTION The invention of the laser two decades ago has changed the direction of research in the physical sciences and created a new field of science--nonlinear optics. At the heart of the theory behind this new discipline is the ability of matter to absorb or emit radiation from an electromagnetic field through higher powers in the electric field. In mathematical language: p* + = 00 X(n)En n=1 in which P is the polarization of the medium interacting with radiation, E is the electric field and x(n) is the complex susceptibility of the material. In general, as n increases the contribution that x(n) makes to the overall absorption or emission of radiation decreases rapidly. In fact, only through the use of the laser can the scientist obtain the field intensity needed to observe nonlinear effects (n>1) of most systems. Among the various nonlinear effects that have been observed are: stimulated Raman scattering1 , coherent anti-Stokes Raman scattering 2 , self-induced transparency3' 4 , superradiance 2 ,5 , and multiphoton transitions2' 5. It is the last of these phenomena to which this thesis is addressed. To be more specific, I shall describe the experiments and calculations that were done by Steinfeld, Brenner and me to unravel the dynamics of multiphoton absorption in the infrared regime by thiophosgene molecules. Although the theory behind all multiphoton processes is derived from one source--the time-dependent Schrddinger equation--certain features of infrared multiphoton absorption (IRMPA) make it amenable to a mathematical treatment that is distinct from multiphoton absorption 10 in other frequency regimes.
Load more

Recommended publications
  • Interstellar Ices and Radiation-Induced Oxidations of Alcohols
    The Astrophysical Journal, 857:89 (8pp), 2018 April 20 https://doi.org/10.3847/1538-4357/aab708 © 2018. The American Astronomical Society. All rights reserved. Interstellar Ices and Radiation-induced Oxidations of Alcohols R. L. Hudson and M. H. Moore Astrochemistry Laboratory, NASA Goddard Space Flight Center, Greenbelt, Maryland, 20771, USA; [email protected] Received 2017 May 2; revised 2018 March 8; accepted 2018 March 9; published 2018 April 18 Abstract Infrared spectra of ices containing alcohols that are known or potential interstellar molecules are examined before and after irradiation with 1 MeV protons at ∼20 K. The low-temperature oxidation (hydrogen loss) of six alcohols is followed, and conclusions are drawn based on the results. The formation of reaction products is discussed in terms of the literature on the radiation chemistry of alcohols and a systematic variation in their structures. The results from these new laboratory measurements are then applied to a recent study of propargyl alcohol. Connections are drawn between known interstellar molecules, and several new reaction products in interstellar ices are predicted. Key words: astrochemistry – infrared: ISM – ISM: molecules – molecular data – molecular processes 1. Introduction 668 cm−1 was produced in solid propargyl alcohol’sIR spectrum after the compound was irradiated with 2 keV Interstellar ices are now recognized as an important comp- electrons (Sivaraman et al. 2015, hereafter SMSB from the onent of the interstellar medium (ISM). The results of multiple coauthors final initials). That IR peak was assigned to benzene infrared (IR) surveys have led to over a dozen assignments of (C H ), which was said “to be the major product from spectral features to molecular ices, with the more abundant 6 6 propargyl alcohol irradiation.” However, a full mid-IR interstellar ices being H O, CO, and CO (Boogert et al.
    [Show full text]
  • Accurate Enthalpies of Formation of Astromolecules: Energy, Stability and Abundance
    Accurate Enthalpies of Formation of Astromolecules: Energy, Stability and Abundance Emmanuel E. Etim and Elangannan Arunan* Inorganic and Physical Chemistry Department, Indian Institute of Science Bangalore, India-560012 *email: [email protected] ABSTRACT: Accurate enthalpies of formation are reported for known and potential astromolecules using high level ab initio quantum chemical calculations. A total of 130 molecules comprising of 31 isomeric groups and 24 cyanide/isocyanide pairs with atoms ranging from 3 to 12 have been considered. The results show an interesting, surprisingly not well explored, relationship between energy, stability and abundance (ESA) existing among these molecules. Among the isomeric species, isomers with lower enthalpies of formation are more easily observed in the interstellar medium compared to their counterparts with higher enthalpies of formation. Available data in literature confirm the high abundance of the most stable isomer over other isomers in the different groups considered. Potential for interstellar hydrogen bonding accounts for the few exceptions observed. Thus, in general, it suffices to say that the interstellar abundances of related species are directly proportional to their stabilities. The immediate consequences of this relationship in addressing some of the whys and wherefores among astromolecules and in predicting some possible candidates for future astronomical observations are discussed. Our comprehensive results on 130 molecules indicate that the available experimental enthalpy
    [Show full text]
  • Exhaustive Product Analysis of Three Benzene Discharges by Microwave Spectroscopy Michael C
    pubs.acs.org/JPCA Article Exhaustive Product Analysis of Three Benzene Discharges by Microwave Spectroscopy Michael C. McCarthy,* Kin Long Kelvin Lee, P. Brandon Carroll, Jessica P. Porterfield, P. Bryan Changala, James H. Thorpe, and John F. Stanton Cite This: J. Phys. Chem. A 2020, 124, 5170−5181 Read Online ACCESS Metrics & More Article Recommendations *sı Supporting Information ABSTRACT: Using chirped and cavity microwave spectroscopies, automated double resonance, new high-speed fitting and deep learning algorithms, and large databases of computed structures, the discharge products of benzene alone, or in combination with molecular oxygen or nitrogen, have been exhaustively characterized between 6.5 and 26 GHz. In total, more than 3300 spectral features were observed; 89% of these, accounting for 97% of the total intensity, have now been assigned to 152 distinct chemical species and 60 of their variants (i.e., isotopic species and vibrationally excited states). Roughly 50 of the products are entirely new or poorly characterized at high resolution, including many heavier by mass than the precursor benzene. These findings provide direct evidence for a rich architecture of two- and three-dimensional carbon and indicate that benzene growth, particularly the formation of ring−chain molecules, occurs facilely under our experimental conditions. The present analysis also illustrates the utility of microwave spectroscopy as a precision tool for complex mixture analysis, irrespective of whether the rotational spectrum of a product species is known a priori or not. From this large quantity of data, for example, it is possible to determine with confidence the relative abundances of different product masses, but more importantly the relative abundances of different isomers with the same mass.
    [Show full text]
  • One-Step Synthesis of Pyridines and Dihydro- Pyridines in a Continuous Flow Microwave Reactor
    One-step synthesis of pyridines and dihydro- pyridines in a continuous flow microwave reactor Mark C. Bagley*1, Vincenzo Fusillo2, Robert L. Jenkins2, M. Caterina Lubinu2 and Christopher Mason3 Full Research Paper Open Access Address: Beilstein J. Org. Chem. 2013, 9, 1957–1968. 1Department of Chemistry, School of Life Sciences, University of doi:10.3762/bjoc.9.232 Sussex, Falmer, Brighton, East Sussex, BN1 9QJ, UK, 2School of Chemistry, Main Building, Cardiff University, Park Place, Cardiff, Received: 05 July 2013 CF10 3AT, UK and 3CEM Microwave Technology Ltd, 2 Middle Slade, Accepted: 11 September 2013 Buckingham, MK18 1WA, UK Published: 30 September 2013 Email: This article is part of the Thematic Series "Chemistry in flow systems III". Mark C. Bagley* - [email protected] Guest Editor: A. Kirschning * Corresponding author © 2013 Bagley et al; licensee Beilstein-Institut. Keywords: License and terms: see end of document. Bohlmann–Rahtz; continuous flow processing; ethynyl ketones; flow chemistry; Hantzsch dihydropyridine synthesis; heterocycles; microwave synthesis; multicomponent reactions; pyridine synthesis Abstract The Bohlmann–Rahtz pyridine synthesis and the Hantzsch dihydropyridine synthesis can be carried out in a microwave flow reactor or using a conductive heating flow platform for the continuous processing of material. In the Bohlmann–Rahtz reaction, the use of a Brønsted acid catalyst allows Michael addition and cyclodehydration to be carried out in a single step without isolation of intermediates to give the corresponding trisubstituted pyridine as a single regioisomer in good yield. Furthermore, 3-substituted propargyl aldehydes undergo Hantzsch dihydropyridine synthesis in preference to Bohlmann–Rahtz reaction in a very high yielding process that is readily transferred to continuous flow processing.
    [Show full text]
  • The Interactions and Reactions of Atoms and Molecules on the Surfaces of Model Interstellar Dust Grains
    The Interactions and Reactions of Atoms and Molecules on the Surfaces of Model Interstellar Dust Grains A thesis submitted for the degree of Doctor of Philosophy Helen Jessica Kimber Department of Chemistry University College London 2016 -I, Helen Jessica Kimber, confirm that the work presented in this thesis is my own. Where information has been derived from other sources, I confirm that this has been indicated in the thesis. Signed, i Abstract The elemental composition of the known universe comprises almost exclusively light atoms (~99.9% hydrogen and helium). However, to date, close to 200 different molecules have been detected in the interstellar medium (ISM) where their distribution is far from uniform. The vast majority of these molecules are contained within vast clouds of gas and dust referred to as interstellar clouds. Within these interstellar clouds, many of the molecules present are formed via gas-phase ion-neutral reactions. However, there are several molecules for which known gas-phase kinetics cannot account for observed gas-phase abundances. As a result, reactions occurring on the surface of interstellar dust grains are invoked to account for the observed abundances of some of these molecules. This thesis presents results of experimental investigations into the interaction and reactions of atoms and molecules on the surface of model interstellar dust grains. Chapters three and four present results for the reaction of (3P)O on molecular ices. Specifically, the reaction of (3P)O and propyne or acrylonitrile. After a one hour dosing period, temperature programmed desorption (TPD), coupled with time-of-flight mass spectrometry (TOFMS), are used to identify (3P)O addition products.
    [Show full text]
  • Reduced Pressure Oxidation of Propargyl Alcohol to Aldehyde; Propynal
    Reduced pressure oxidation of propargyl alcohol to aldehyde; Propynal Nov 15, 2013 John MacMillan ([email protected]) Chemicals Used Propargyl alcohol, 99%, Aldrich, P5,080-3, redistilled Chromium (VI) oxide, 99+%, Aldrich, 20,782-9 Sodium Chloride, 99%*%, A.C.S. reagent, Aldrich, 22,351-4 Sulfuric acid, 95-98%, A.C.S. Reagent, Aldrich, 25.810-5 Procedure This material was prepared by a modification of the Organic Synthesis procedure. See lead reference. To a 2 liter three neck flask, equipped with a mechanical stirrer, and ice/salt bath was charged 120 g ((2.14 mole) redistilled propargyl alcohol and 240 ml of water. To this mixture was then added a cooled solution of 135 ml concentrated sulfuric acid in 150 ml of water. A "Y" tube was inserted in one neck of the flask and a pressure equalized dropping funnel was placed in one neck of the "Y" tube. The other neck of the "Y" tube lead to two traps, in series, which in turn were connected to a McLeod pressure gage and vacuum pump. The third neck of the flask was connected to a fine capillary which served as a nitrogen inlet. A cooled solution of 210 g chromium trioxide, 200 ml of water and 100 ml concentrated sulfuric acid was then added to the dropping funnel. One trap was cooled to ~ - 10° with an ice/salt mixture and the second trap was cooled with a dry ice/acetone bath to ~ -78°C. The exterior of the 2 liter flask was cooled to ~ - 10°C with ice/salt.
    [Show full text]
  • Supplement of Measurement Report: Important Contributions of Oxygenated Compounds to Emissions and Chemistry of Volatile Organic Compounds in Urban Air
    Supplement of Atmos. Chem. Phys., 20, 14769–14785, 2020 https://doi.org/10.5194/acp-20-14769-2020-supplement © Author(s) 2020. This work is distributed under the Creative Commons Attribution 4.0 License. Supplement of Measurement report: Important contributions of oxygenated compounds to emissions and chemistry of volatile organic compounds in urban air Caihong Wu et al. Correspondence to: Bin Yuan ([email protected]) and Min Shao ([email protected]) The copyright of individual parts of the supplement might differ from the CC BY 4.0 License. 24 1. Sensitivity of VOCs in PTR-MS 25 Proton-transfer-reaction time-of-flight mass spectrometry (PTR-TOF-MS) allows 26 the detection of a large number of VOCs in air through proton-transfer reaction with 27 H3O+ reagent ions and detection by a mass spectrometer. Measurement sensitivities can 28 be experimentally determined using calibration gases, but only the sensitivity of few 29 species can be obtained. For other species, the sensitivity can be calculated using the 30 rate constant for the proton-transfer reaction. 31 In PTR-ToF-MS, VOCs that have higher proton affinity than water will be ionized + 32 via proton transfer with H3O to produce the product ions. + + 33 VOC+H3O → VOC·H +H2O 34 According to the reaction rate equation, the concentration of VOC•H can be 35 calculated as follows: + 36 VOC·H=H3O 0(1-exp(-[VOC]∆)) + + 37 Where k is the reaction rate constant, [H3O ]0 is the signal of H3O ions before 38 reaction, [VOC] is the number concentration of the VOC in the drift tube, and Δt is the + 39 reaction time for H3O traversing the drift tube.
    [Show full text]
  • 27 May 2021 Given by Tercero Et Al
    Astronomy & Astrophysics manuscript no. aa41297 ©ESO 2021 May 28, 2021 Letter to the Editor The sulphur saga in TMC-1: Discovery of HCSCN and HCSCCH ? J. Cernicharo1, C. Cabezas1, Y. Endo2, M. Agúndez1, B. Tercero3; 4, J. R. Pardo1, N. Marcelino1, P. de Vicente3 1 Grupo de Astrofísica Molecular, Instituto de Física Fundamental (IFF-CSIC), C/ Serrano 121, 28006 Madrid, Spain e-mail: [email protected],[email protected] 2 Department of Applied Chemistry, Science Building II, National Yang Ming Chiao Tung University, 1001 Ta-Hsueh Rd., Hsinchu 30010, Taiwan 3 Centro de Desarrollos Tecnológicos, Observatorio de Yebes (IGN), 19141 Yebes, Guadalajara, Spain 4 Observatorio Astronómico Nacional (IGN), C/Alfonso XII, 3, 28014, Madrid, Spain Received; accepted ABSTRACT We report the detection, for the first time in space, of cyano thioformaldehyde (HCSCN) and propynethial (HCSCCH) towards the starless core TMC-1. Cyano thioformaldehyde presents a series of prominent a- and b-type lines, which are the strongest previously unassigned features in our Q-band line survey of TMC-1. Remarkably, HCSCN is four times more abundant than cyano formaldehyde (HCOCN). On the other hand, HCSCCH is five times less abundant than propynal (HCOCCH). Surprisingly, we find an abundance ratio HCSCCH/HCSCN of ∼ 0.25, in contrast with most other ethynyl-cyanide pairs of molecules for which the CCH-bearing species is more abundant than the CN-bearing one. We discuss the formation of these molecules in terms of neutral-neutral reactions of S atoms with CH2CCH and CH2CN radicals as well as of CCH and CN radicals with H2CS.
    [Show full text]
  • 31295005227565.Pdf (11.48Mb)
    VIBRATIONAL ANALYSIS AND AB INITIO STUDIES OF PROPIOLIC ACID by EDMUND MOSES NSO NDIP, B.S., M.S. A DISSERTATION IN CHEMISTRY Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY Approved August, 1987 ACKNOWLEDGEMENTS My educational experiences at Texas Tech University have been very rewarding and along the way, I have had the good fortune of being associated with a lot of people. Consequently, I am indebted to them and wish to express my sincere gratitude for their help. First of all, I wish to thank Professor R. L Redington, my research mentor, for his ever enduring support, guidance and patience throughout the course of my study. My special thanks also go to Professor R. E. Wilde, Jr. for his friendship throughout the years. To the members of my committee, I say thank you for your patience. My thanks also go to Dr. J. L Mills, Dr. R. D. Larsen, and Dr. Jim Liang and his associates at the University of Utah, Chemistry Department. I do recognize here the goodwill of Prof. Josef MichI of the University of Texas at Austin (formerly of the University of Utah). Financial support was received from Texas Tech University and the Robert Welch Foundation. I must thank the government and people of Cameroon for the scholarships given me throughout the many years of my education. To my kids, Edmund, Jr. and Laura, I say thanks for the smiles throughout the difficult moments that we all shared. I especially thank my wife, Grace Manyi Ndip, for the sacrifices she has made over the years and for her help in preparing parts of this dissertation.
    [Show full text]
  • The Interstellar Chemistry of H2C3O Isomers
    The interstellar chemistry of H2C3O isomers. Jean-Christophe Loison1,2*, Marcelino Agúndez3, Núria Marcelino4, Valentine Wakelam5,6, Kevin M. Hickson1,2, José Cernicharo3, Maryvonne Gerin7, Evelyne Roueff8, Michel Guélin9 *Corresponding author: [email protected] 1 Univ. Bordeaux, ISM, UMR 5255, F-33400 Talence, France 2 CNRS, ISM, UMR 5255, F-33400 Talence, France 3 Instituto de Ciencia de Materiales de Madrid, CSIC, C\ Sor Juana Inés de la Cruz 3, 28049 Cantoblanco, Spain 4 INAF, Osservatorio di Radioastronomia, via P. Gobetti 101, 40129 Bologna, Italy 5 Univ. Bordeaux, LAB, UMR 5804, F-33270, Floirac, France. 6 CNRS, LAB, UMR 5804, F-33270, Floirac, France 7 LERMA, Observatoire de Paris, École Normale Supérieure, PSL Research University, CNRS, UMR8112, F-75014, Paris, France 8 LERMA, Observatoire de Paris, PSL Research University, CNRS, UMR8112, Place Jules Janssen, 92190 Meudon, France 9 Institut de Radioastronomie Millimétrique, 300 rue de la Piscine, 38046, St. Martin d’Heres, France We present the detection of two H2C3O isomers, propynal and cyclopropenone, toward various starless cores and molecular clouds, together with upper limits for the third isomer propadienone. We review the processes controlling the abundances of H2C3O isomers in interstellar media showing that the reactions involved are gas-phase ones. We show that the abundances of these species are controlled by kinetic rather than thermodynamic effects. 1 Introduction The formation of Complex Organic Molecules (COMs) in interstellar media, particularly in dense molecular clouds, is a challenging issue. Until recently, the paradigm has been that COMs were formed on grains through surface chemistry (Tielens & Hagen 1982) and then released into the gas-phase in warm environments through thermal desorption (Herbst & Van Dishoeck 2009).
    [Show full text]
  • Nomination Background: Propargyl Alcohol (CASRN: 107-19-7)
    SUMMARY OF DATA FOR CHEMICAL SELECTION PROPARGYL ALCOHOL CAS No. 107-19-7 BASIS OF NOMINATION TO THE CSWG The nomination of propargyl alcohol to the CSWG is based on high production volume, exposure potential, and suspicion of potential carcinogenicity. Dr. Elizabeth Weisburger, a member of the American Conference of Governmental Industrial Hygienists (ACGIH) TLV Committee as well as the Chemical Selection Working Group (CSWG), provided a list of 281 chemical substances with ACGIH recommended TLVs for which there were no long-term studies cited in the supporting data and no designations with respect to carcinogenicity. She presented the list to the Chemical Selection Planning Group (CSPG) for evaluation as chemicals which may warrant chronic testing; it was affirmed at the CSPG meeting held on August 9, 1994, that the 281 "TLV Chemicals" be reviewed as a Class Study. As a result of the class study review, propargyl alcohol is presented as a candidate for testing by the National Toxicology Program because of: • potential for occupational exposures based on moderately high production volume • evidence of occupational exposures based on TLV and other literature documentation • potential for human exposures based on hazardous waste occurrences in environmental media • suspicion of carcinogenicity based on mixed results in available short-term assays for genetic toxicity and liver and kidney changes in subchronic mammalian toxicity studies • lack of chronic toxicity data. Sources of human exposure to propargyl alcohol are mainly occupational; and the exposure potential is considered moderate based on an estimated U.S. annual production volume range of 0.5 to 2.8 million pounds, an estimate of 54,358 worker exposures (19,933 female) reported in the NOES database, and characterization of propargyl alcohol as a moderately volatile liquid identified in air, water, and soil.
    [Show full text]
  • The Complex Chemistry of Outflow Cavity Walls Exposed: the Case Of
    Mon. Not. R. Astron. Soc. 000, 1–21 (2015) Printed 18 June 2018 (MN LATEX style file v2.2) The complex chemistry of outflow cavity walls exposed: the case of low-mass protostars Maria N. Drozdovskaya1⋆, Catherine Walsh1, Ruud Visser2, Daniel Harsono1,3 and Ewine F. van Dishoeck1,4 1 Leiden Observatory, P.O. Box 9513, 2300 RA, Leiden, The Netherlands 2 European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany 3 SRON Netherlands Institute for Space Research, P.O. Box 800, 9700 AV Groningen, The Netherlands 4 Max-Planck-Institut f¨ur Extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany Accepted 2015 May 20. Received 2015 May 7; in original form 2015 March 18 ABSTRACT Complex organic molecules are ubiquitous companions of young low-mass protostars. Recent observations suggest that their emission stems, not only from the traditional hot corino, but also from offset positions. In this work, 2D physicochemical modelling of an envelope-cavity system is carried out. Wavelength-dependent radiative transfer calculations are performed and a comprehensive gas-grain chemical network is used to simulate the physical and chemical structure. The morphology of the system delineates three distinct regions: the cavity wall layer with time-dependent and species-variant enhancements; a torus rich in complex organic ices, but not reflected in gas-phase abundances; and the remaining outer envelope abundant in simpler solid and gaseous molecules. Strongly irradiated regions, such as the cavity wall layer, are subject to frequent photodissociation in the solid phase. Subsequent recombination of the photoproducts leads to frequent reactive desorption, causing gas-phase enhancements of several orders of magnitude.
    [Show full text]