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Title: The fragmentation of molecules and ions
Author: Sweeney, C. W.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1983
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The work described in this thesis comprises two studies related to gas phase processes: a theoretical study of negative ion mass spectral processes at low electron energies, and an experimental investigation into the hydropyrolysis of ethylbenzene. In Part One, the MINDO/3 quantum chemical method has been used to study the fragmentation processes of open and closed shell organic anions. The principal aims of the study were threefold: to assess the accuracy of MINDO/3 for carbanions; to determine the relevance of the calculations to mass spectral processes, and to deduce the mechanisms giving rise to the spectra for some alcohols and carbonyl compounds. The following are the main conclusions drawn from the study. (1) No obvious correlations exist between the equilibrium properties of the ions and their fragmentation modes. (2) The accuracy of calculated activation energies is as good as would be expected of the species for which MINDO/3 was parameterized. (3) The charge is localized in the products such that the lowest enthalpy of reaction obtains. (4) The mass spectra arc derived from molecular ions formed initially in excited electronic states; but these states are not necessarily isolated from the ground state. (5) There is evidence from the observed spectra and the MINDO/3 results that unimolecular rate theory is applicable to dissociative resonance capture. (6) Fragmentation rate calculations corroborate the anomalous result that some simple fission processes have exceptionally high reverse activation energies. (7) The deduced mechanisms are able to account for the observed spectra, except at high energies; which implies that activation energies cease to be pertinent factors at these energies. The hydropyrolysis of ethylbenzene was investigated over the temperature range 530-581°C. Six products were identified and quantitatively determined: benzene, toluene, styrene, ethane, echene and mccyane_1 The following Arrhenius parameters were estimated: E ° 71.0 kcal mol- and A - 10 .Is-1. On the basis of the experimental results and thonmochemical data, the mechanism for this complex reaction is discussed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available