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.
RSO₂ —» R + SO₂
RS0₂ + 02 —» RS0₂0₂
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.
