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Title: Kinetics of the reactions of free radicals and ions in the gas phase
Author: Thynne, John Corelli James
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1969
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The work described in this thesis represents the results of investigations in the field of gas phase kinetics carried out at the Universities oi Edinburgh, Leeds, Toronto and California, the National Research Council of Canada, Ottawa, and the Ministry'of Aviation, Waltham Abbey. The thesis has been divided into two sections; investigations oi free radicals are described in the first section and of ions in the second. The work on free radicals has been mainly concerned with the reactions of alkyl, fluoroalkyl and alkoxyl radicals. Emphasis has been placed on the quantitative aspects of their reactions and some one hundred and forty rate constants and Arrhenius parameters have been reported. The radical-sensitised-deoomposition oi various formate esters has been used to generate thermally-equilibrated alkyl radicals, and data obtained for the auto- and cross-combination and disproportionation reactions for several pairs of alkyl radicals as well as for several hydrogen atom abstraction reactions. Deuterium labelling has enabled tho precise position of radical attack on molecules containing more than one functional group to be determined and in several cases primary and secondary isotope effects have been evaluated. By selection of a range of nitrogen-cont&ixiing compounds information has been obtained regarding the effects of molecular environment upon the reactivity of molecules towards radical attack. In addition, this work ha3 yielded data for the reactions of amino radicals with alkanes which otherwise would have been difficult to obtain. Methoxyl radicals have been generated by means of the photodecomposition of methyl formate and of dimethyl carbonate. Kinetic data were measured for hydrogen atom abstraction from the radical sources by Use other side if necessary. methoxyl radicals, for the auto-disproportionation of the radicals and for their reactions with methyl and forrayl radicals, A mass-spectrometric study of the thermal decomposition of dialkyl peroxides enabled estimates to be made of the heats of formation of ethoxyl and iso-propoxyl radicals and the apparent anomaly in the thermochemistry of the ethoxyl radical has been resolved. The unimolecular decomposition by C-C bond fission of the ethoxyl, iso-propoxyi and tert-butoxyl radicals has been studied. For the isopropoxyl and tert-butoxyl radicals the decomposition reaction was shown to be pressure dependent and, by means of a Hinshelwood-Lindemann treatment, Arrhenius parameters were calculated for the high- and low pressure limiting rates. Section two is concerned with the application of mass spectrometry to the study of ion-molecule reactions and also to the investigation of negative ion formation by molecules as a result of electron impact, particularly with low energy electrons. Some sixty ion-molecule reactions involving hydrogen atom or proton transfer have been studied. In many oases deuterium labelling has been used to determine the identity of the reactant ion and the site of attack on the molecule. Reaction cross-sections and rate constants have been measured under constant repelier field conditions (where the reactant ions have a range of energies) and also under zero-field conditions (where the reactions studied are due to thermal energy ions). Rate constants were calculated using an ion-induced dipole model but, particularly for polar molecules, agreement between the experimentally-measured and theoretically-predicted results was poor. An improved correlation was obtained when the model included ion-permanent dipole interactions. Studies of the electron energy dependence of negative ion formation by various molecules have been made and several new ions identified. Electron aifinities of the trifluoromethyl, pentafluoroethy1 and trifluoroucetyl radicals have been estimated and values deduced for G-G and G-F bond dissociation energies in hexafluoroacetone and hexafluoroethane. Secondary electron capture has been shown to be responsible for formation of the molecule-ion of hexafluoroacetone, the secondary electrons being produced in the ionisation process leading to the formation of CF₃COCF₃⁺. Fluoride ion formation at 12.5eV for hexafluoroethane has also been shown to be the result oi secondary electron capture. The process responsible for secondary electron formation differed from that for hexafluoroacetone, in that,although the secondary electron was produced by collision of a primary electron with hexafluoroethane, an electronically excited state of hexafluoroethane was formed rather than an ionised molecule.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (D.Sc.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available