This thesis describes work conducted using a linear time-of-flight (TOF) mass spectrometer concerning the gas phase reactivity of atomic and small molecular doubly charged positive ions (dications) with neutral species at low collision energies (below 20 eV). The process of analysis by which measured ion intensities gathered using this instrument are converted into reaction cross-sections is completely redeveloped, permitting for the first time the cross-sections of all ionic products of bimolecular reactions to be derived. The new methodology calculates reaction cross-sections in arbitrary units furthermore the absolute size of these arbitrary units depends only on the absolute value of the number density distribution of the neutral reactant and thus is independent of collision energy and changes from one collision system to another only due to differences in the effusive properties of the neutral reactant. While a number of collision systems have been observed, three were selected for more rigorous study: SF2+ + Ar, Cl2+ + CO and HC12+ + CO, and these are reported herein. The first and second of these collisions are particularly novel because their chemistry includes reaction channels that produce a doubly charged product 2"1" 2"F containing new chemical bonds (ArS and CC1 respectively). This class of dication- neutral reaction is highly unusual and only a very limited number of examples have been reported previously. The chemistry of HC1 with CO, while bearing similarities to that of Cl2+, also exhibits proton transfer (to form HCO+) that occurs with a branching ratio similar to electron transfer. The new procedure of analysis is applied to each system, allowing calculation of the reaction cross-sections for all charged products and is demonstrated to perform suitably well. The mechanism of electron transfer in dication-neutral systems is well understood, and computational calculations are conducted to complement the experimental results, but consideration of energetics also allows the observation of bond-forming products to be rationalized. The development of a more satisfactory means of extracting reaction cross- sections from experimental measurements, while an achievement, has highlighted a number of shortcomings in the present experimental design and a number of suggestions have also been made for a future upgrade of the experiment that would facilitate simpler analysis as well as improved resolution and flexibility.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:498287 |
| Date | January 2007 |
| Creators | Burnside, Paul William |
| Publisher | University College London (University of London) |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://discovery.ucl.ac.uk/1445337/ |
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