The investigation of gas-phase ion-molecule reactions with fourier transform ion cyclotron resonance mass spectrometry

Citation

Crellin, Kevin Christopher (1997) The investigation of gas-phase ion-molecule reactions with fourier transform ion cyclotron resonance mass spectrometry. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/p8bs-x927. https://resolver.caltech.edu/CaltechTHESIS:10222009-123129177

Abstract

The gas-phase chemistry of several chemical systems have been investigated with Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. The emphasis of these experiments is on organoscandium ion chemistry, but inorganic and organic systems have also been examined. Furthermore, quantum mechanical calculations have been performed on selected systems to help in the interpretation of the experimental data or guide the experiments. Chapter 1 is a brief review of the experimental aspects of FT-ICR mass spectrometry. The history of the development of FT-ICR is given, and the instrumentation required to perform FT-ICR mass spectrometry is described. The mathematical description of ion motion is discussed, and applied to the description of the excitation and detection of ions. A short explanation of how these aspects are combined to form a standard experimental event sequence is then presented. Chapters 2-5 present the results of our investigations of the reactivity of organoscandium ions with alkanes and alcohols. In Chapter 2 we examine the reactions of Sc(CH_3)_2^+ with methane, ethane, [2,2-D_2]-propane, [1,1,1,4,4,4-D_6]-n-butane and [2- D]-isobutane, while in Chapter 3 the reactions of CH_3ScCH_2CH_3^+ with methane, ethane, [2,2-D_2]-propane, [1,1,1,4,4,4-D_6]-n-butane, [2-D]-isobutane and n-pentane are observed. In both systems σ-bond metathesis reactions similar to those observed in liquid-phase systems are seen. Site selectivity with the larger alkanes is also observed with the aid of deuterium labeling. In Chapter 4 we return to the Sc(CH_3)_2^+ ion and investigate its reactivity with cyclopentane and cyclohexane. Once again, σ-bond metathesis reactions are observed, this time with secondary C-H bonds rather than primary C-H bonds (as seen with the straight- and branched-chain hydrocarbons). We then change our focus in Chapter 5 to the σ-bond metathesis reactions of Sc(OCD_3)_2^+ with water, ethanol and 1-propanol. Again, σ-bond metathesis reactions were seen. However, in this case ligand exchange equilibria were observed via σ-bond metathesis and used to evaluate the relative bond energies of various Sc^+ alkoxide bonds. Chapters 6-8 move away from organoscandium systems and into various inorganic and organic systems. In chapter 6 the reaction of Cl^- with C1ONO_2 is examined. This reaction was found to be fast and efficient in the gas phase, which raises the possibility that Cl^- might react directly with C1ONO_2 on water ice films on the surface of type II polar stratospheric cloud particles. Chapter 7 investigates the reactions of nitrobenzene and the explosives 2,4,6-trinitrotoluene (TNT) and 1,3,5-trinitro-1,3,5- triazacyclohexane (RDX) with Si(CH_3)_3^+. Adduct formation and small amounts of characteristic fragmentation (with the TNT and RDX adducts) is observed, suggesting that these types of reactions could be useful as a detection scheme for common explosives. Chapter 8 extends this work to the explosives EGDN (ethylene glycol dinitrate) and PETN (pentaerythritol tetranitrate). These nitrate ester explosives do react with Si(CH_3)_3^+, but no molecular adduct is seen in the FT-ICR mass spectrometer. However, characteristic fragment ions are seen and the PETN-Si(CH_3)_3^+ adduct can be seen in a sector mass spectrometer. The differences in the reactivity of nitro explosives and nitrate ester explosives are also discussed.

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