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Studies of atomic and molecular cations

Atomic and molecular cations have the potential to strongly influence a number of industrial, atmospheric and interstellar environments in which they are expected to be present. As a result, information on the generation and reactivity of positively charged species is invaluable when attempting to model and understand the physical and chemical processes taking place in such surroundings. This thesis reports a number of experimental investigations of the formation and reactivity of atomic and molecular cations. Firstly, a detailed study of the electron ionisation of sulphur dioxide (SO2) is presented. Relative precursor-specific partial ionisation cross sections for the fragment ions formed following electron ionisation of sulphur dioxide have been measured using time-of-flight mass spectrometry coupled with ion coincidence detection. These data quantify, for the first time, the formation of all fragment ions, relative to the formation of SO2+, via single, double and triple electron ionization of SO2. Secondly, the investigations of the bimolecular reactivity of a number of doubly (I2+ and N22+) and triply charged (I3+, Xe3+, CS23+) reactants are presented. A crossed-beam mass spectrometer was used to identify ion-molecule reaction products. The doubly and triply charged (I2+ and I3+/Xe3+) reactants are shown to participate in processes involving substantial rearrangement of chemical bonds. This reactivity can be encapsulated using a simple electrostatic model and energetic arguments. Furthermore, the same model has been updated to account for the results observed following the reactions of atomic trications. A different mass spectrometer, equipped with a position-sensitive coincidence ion detector, was then used to explore the dynamics of reactions involving first a molecular dication (N22+) with various low-mass organic molecules and then atomic (Xe3+) and molecular trications (CS23+). Product ion velocities determined using this technique can be used to explore the reaction energetics and angular scattering distributions for individual ion-molecule reaction channels. In turn, the interpretation of these data allow the identification of reaction mechanisms. The range of reactions exhibited in all of these studies is surprisingly diverse, clearly indicating a complex chemistry for collision systems involving dicationic and tricationic reactants.
Date January 2014
CreatorsFletcher, James
PublisherUniversity College London (University of London)
Source SetsEthos UK
Detected LanguageEnglish
TypeElectronic Thesis or Dissertation

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