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Gas Phase Synthesis of Interstellar Cumulenes. Mass Spectrometric and Theoretical Studies."

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Gas Phase Synthesis of Interstellar Cumulenes. Mass Spectrometric and Theoretical Studies. rl ì 6. .B,1l thesis titled: "Gas Phase Synthesis of Interstellar Cumulenes. Mass Spectrometric and Theoretical studies." submitted for the Degree of Doctor of Philosophy (Ph.D') by Stephen J. Blanksby B.Sc.(Hons,) from the Department of ChemistrY The University of Adelaide Cì UCE April 1999 Preface Contents Title page (i) Contents (ii) Abstract (v) Statement of OriginalitY (vi) Acknowledgments (vii) List of Figures (ix) Phase" I Chapter 1. "The Generation and Characterisation of Ions in the Gas 1.I Abstract I 1.II Generating ions 2 t0 l.ru The Mass SPectrometer t2 1.IV Characterisation of Ions 1.V Fragmentation Behaviour 22 Chapter 2 "Theoretical Methods for the Determination of Structure and 26 Energetics" 26 2,7 Abstract 27 2.IT Molecular Orbital Theory JJ 2.TII Density Functional Theory 2.rv Calculation of Molecular Properties 34 2.V Unimolecular Reactions 35 Chapter 3 "Interstellar and Circumstellar Cumulenes. Mass Spectrometric and 38 Related Studies" 3.I Abstract 38 3.II Interstellar Cumulenes 39 3.III Generation of Interstellar Cumulenes by Mass Spectrometry 46 3.IV Summary 59 Preface Chapter 4 "Generation of Two Isomers of C5H from the Corresponding Anions' 61 ATheoreticallyMotivatedMassSpectrometricStudy.'. 6l 4.r Abstract 62 4.rl Introduction 66 4.III Results and Discussion 83 4.IV Conclusions 84 4.V Experimental Section 89 4.VI Appendices 92 Chapter 5 "Gas Phase Syntheses of Three Isomeric CSHZ Radical Anions and Their Elusive Neutrals. A Joint Experimental and Theoretical Study." 92 5.I Abstract 93 5.II Introduction 95 5.ru Results and Discussion t12 5.IV Conclusions 113 5.V Experimental Section ttl 5.VI Appendices t20 Chapter 6 "Gas Phase Syntheses of Three Isomeric ClHz Radical Anions and Their Elusive Neutrals. A Joint Experimental and Theoretical Study." t20 6.I Abstract 12l 6.II Introduction r23 6.III Results and Discussion t42 6.IV Conclusions t43 6.V Experimental Section r46 6.VI Appendices 111 Preface of 155 Chapter 7 "The Gas Phase Synthesis of and Unimolecular Behaviour NCCCN.'' t55 7.I Abstract 156 7.IÍ Introduction 160 7.III Results and Discussion r85 7.IV Summary 187 7.V ExPerimental Section 190 7.VI APPendices r93 Chapter I "Summary and Conclusions" r93 8.I Theoretical Calculations r95 8.II Mass SPectrometric Studies r97 8.Itr Potential Interstellar Molecules? References r99 Published PaPers (xiii) IV Preface Abstract gas Astrophysics has identified a range of fascinating molecular species residing in the large of the more clouds which are present in regions of interstellar and circumstellar space. Some here interesting of these are hydrocarbon cumulenes of the form CnH and CnH2' We present the gas methodologies for the synthesis of charged analogues of a number of these species in to phase. These ions have been subjected to neutralisation reionisation mass spectrometry establish the stability of the corresponding neutrals on the mass spectrometric timescale' These studies represent some of the first terrestrial observations of such cumulenes and further investigation has yielded novel homologues and structural isomers' Quantum chemical calculations have been employed in this study to provide further insight into the structure and energetics of these unusual molecules. Preface Acknowledgments people and organisattons A thesis such as this cannot be produced in isolation' Many other work presented here' It is have been involved with providing assistance and support for the necessary, and also appropriate to acknowledge their contributions' H' Bowie' Firstly, I would like to sincerely thank my PhD supervisor Professor John and exciting Professor Bowie has provided the opportunity for me to work in a fascinating phase ion-chemistry is area of chemistry. His knowledge of, and enthusiasm for, gas during my infectious and his strong work ethic has been highly motivating to me for me to candidature. I am also grateful to Professor Bowie for creating opportunities me to attend participate in the larger scientific community. He has made it possible for and overseas' The conferences and collaborate in research with colleagues, both in Australia and I certainly time I have spent under Professor Bowie's supervision has been inspiring hope to carry many of his attitudes into my future career' presented in I would also like to thank Dr Suresh Dua for his contributions to the research my studies' this thesis as well as for his continued wisdom and encouragement throughout out and prepared Suresh guided much of the condensed phase synthetic work which I carried me a great deal some of the less stable precursors. He was also responsible for teaching acknowledge the about fhe ZAB 2HF mass spectrometer. In this regard, I would also like to great deal contributions of Tom Blumenthal and Rob Pearce who have both taught me a about mass spectrometry, My knowledge of computational techniques has been ably of their time assisted by Mark Taylor and Dr Mark Buntine who have both given generously to help me with theoretical calculations. the Bowie In a general sense, I would like to acknowledge past and present members of members willing research group. In my four years with the group I have always found other Preface to help with large or small problems as well as providing a relaxed but focussed working environment. In particular I would like to thank, Dr Simon Steinborner, Dr John Hevko, paul Wabnitz, C.S. Brian Chia, Tom Rozek and Mark Taylor. I am also thankful to Professor Helmut Schwarz and members of his research group at the Technical University of Berlin. My four month sabbatical there advanced my knowledge of chemistry substantially and motivated much of my subsequent research. I would like to mention in particular, Dr Detlef Schröder, Dr Georg Hornung, Dr Christoph Schalley and Dr Jeremy Harvey who have all contributed to the science presented in this thesis. I would like to express my appreciation to those people who have spent many hours proof reading parts or the whole of this thesis. These patient individuals were Professor Bowie, Dr Suresh Dua, Sam Peppe, Dr Mark Buntine and Peter Turner. Thanks must also go to the Department of Chemistry at the University of Adelaide. The academic, research and technical staff as well as my fellow students have readily provided their time, advice and assistance for all range of matters. I have enjoyed the working and social environment within the Department in my time here as a postgraduate student. I also acknowledge the University of Adelaide for providing administrative and financial assistance, particularly for the award of an Overseas Travel Grant and a George Murray Scholarship to support my visit to the Berlin laboratories in 1997. On further financial matters, I am appreciative of the support Australian Postgraduate Awards for awarding me ¿l postgraduate stipend for the years 1996-1999. vilt Preface List of Figures Figure I.l Stylised Morse potential cu Vertical ionisation of ih;;;h*l by'electron impact (EI) resu (bound) radical catiott AB'+ and (b)1, an unbound potential surface ¡' to a neutral radical A' and the even electron cation B+ (dissociative ionisation)' Figure t,2 A simplified schematic representation of the VG ZAB 2HF (FFR refers to field-free region). Figure I.3 A simptified schematic depicting the neutralisation reionisation process. Figure 1.4 Franck-Condon diagrams illustrating the effects of the vertical electrott transitions in a +NR+ experiment: (a) represents the situation where the geometries oJ AB and AB+ are similar whilst in (b) the structures are dffirent.60 Figure 1.5 The experimental aryangement for an NCR experiment. Figure 1.6 (a) -NR+, (b) -Cn+ and (c) -NIDD+ spectra for the formate anion (HCOz- ).66 Figure 2.L The reaction coordinate diagram for the idealised unimolecular rearrangetnent of ABC to ACB Figure 3.1 Contour depiction of the annular distribution o! {q)^y-Ç:N and (b) C jN in the ciicumstellar envelopr'rrrrourãing the red giant star IRC+10216. The darker shacling represents regions of higher molecular density.l?s -C=CCH2OCH Figure 3.2 The collisional activation MIKE spectrum of j'|43 Peaks ctt */, 37,38 and 39 correspond to the anionic species, C2CH, CZCHZ and CZCH-¡ respectively. Figure 3.3 Comparison of the NR spectra of (a) CsCHz'- (-lfR*,¡ and (b) HCall'+ (*ÑR*). It is significant to note the low abundance of peaks corresponding to fragntents oJ' the type CrHr'+ in specyum (a) compared to specyu* (Ð.153 Figure 4.1 Optimised geometries for (a) triplet and (b) singlet electronic states of CaCH- (1'). These geometies were calculated at the B3LYP/aug-cc-pVDZ level of theory. All bond lengths are given in angstroms and all angles in degrees. IX Preface mol-1, with zero-point energy contributions included' geometry Figure 4.3 Optimised g-e-o-ryy?lA for thg state of HC.zC¡. (2-)' llt.gro.un! Att bond lengths'The are given in was calculated at tti*n"srvil"ís_lrr_pvoz'tävet of rheory." angstroms and all angles in degrees' geometry Figure 4.4 Optimised g-eo_rnetry for thei!'.Sroynd state of C2C jH-.{3-) .The bond lengths are given in was calculared at ti-r*a"srviloí! cr-pvDZ livet of theory." All ongstroms and all angles in degrees' geomefil Figure 4.5 Optimised geomet.ry for the-l!1 ground state of CZ9llCz: .Ø-)' .The rengths are given irt was carcurated at äl Êilip/írþ-cc-pvDi iever of theory". Nr bond angstroms and all angles in degrees' (u) Figure 4.6 -CR+ (oz, 807o T; O2, 807o r) spectra of m/z 6l .from TMSC:CC=CCH2oCHj,givingCaCH-and(b)HC=CCH(oC)CHzCHj)C=CHgivittg and C,,.+, C2CHC2-. These spectra both show frasments of the forms CnH+ (a) Figure 4.7 -NR + (oz, 807o T; O2, 807o r) spectra of m/z 6l .from TMSC:CC=CCH2TCHj,givingC¿CH-and(b)HC:CCH(oCoCHzCHj)C=CHgiving and C,,.+.
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