Studies of some gas-phase oxidation reactions using electron spectroscopy and the electronic structure of some small molecules

Wright, Timothy Grahame (1991) Studies of some gas-phase oxidation reactions using electron spectroscopy and the electronic structure of some small molecules. University of Southampton, Doctoral Thesis.

Abstract

Most of this thesis is concerned with recording electron spectra arising either from photoionisation of gas-phase neutral molecules or from gas-phase chemi-ionisation reactions. The experimental techniques used, especially those involved with the use of high temperature evaporations are detailed in the early part of the thesis. Ab initio molecular orbital calculations were used in the interpretation of some of the photoelectron spectra.

Chemi-ionisation reactions arising from the gas-phase oxidation of acetylene have been studied in some detail by recording chcmielcctron spectra for this reaction under a range of experimental conditions. The interpretation of the spectra was based largely on thermodynamic data and comparison with the results of previous work. Some general comments on the relevance of these studies to flame chemistry arc made.

Studies of chemi-ionisation reactions which occur in the gas-phase oxidation of some lanthanide metals have also been performed using chemi-electron spectroscopy and chcmi-ion mass spectromctry. The use of approximate kinetic modelling of the reaction scheme, together with the experimental electron spectroscopic and mass spectrometric data, allowed information on the reactions to be obtained. The electron and ion spectra obtained were rationalised in terms of available thermodynamic data.

The production of alkali metal monoxides (NaO and KO) in the gas-phase by use of the reaction between an alkali metal vapour and the oxidants Os or N2O allowed the low energy region of the UVPES of these metal oxides to be recorded. Assignment of the observed bands was achieved by the use of ab initio molecular orbital calculations. For M = Na and K, a band was seen from the M plus Os reaction that was not seen in the M plus N2O reaction. This band was assigned to the first ionisation of MO2 (M= Na, K). Preliminary spectra of LiO formed from the reaction of Li with N2O are also reported.

Ab inilio calculations of the equilibrium geometries and vibrational frequencies of the alkaline earth dihalides BeF2, MgF2 and CaF2 have been performed.

The effect of basis set superposition error (BSSE) on the calculated equilibrium bond angle in CaF2 has been studied, and the effects of BSSE on the calculated dissociation energies of the alkali monoxides NaO and KO have also been investigated.

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