In this thesis the processes responsible for the
formation of negative ions by the interaction of low energy
electrons (0 to 15eV) with molecules in the gas phase have
been investigated. Particular attention has been paid to
the processes known as associative resonance capture and
dissociative resonance capture. For a molecule AB,
associative resonance capture is described by the equation
AB + e → AB⁻, where the metastable molecular negative ion
AB⁻ is formed by the capture of slow electrons.
Dissociative resonance capture, described by the equation
AB⁻ → A⁻ + B, results in the formation of a stable negative
ion and can occur throughout the energy range studied.
A historical review of the theoretical approach to
electron-attachment is followed by detailed accounts of
the most recent theoretical treatments of associative and
dissociative resonance capture. The time-of-flight mass
spectrometer used for this study has been described in some
detail as have the experimental procedures developed. The
various devices used to overcome the problems created by the
broad electron energy distribution, which is due to the use
of thermionically emitted electron beams, have been critically
reviewed and the analytical deconvolution procedure adopted
in this study has been described in detail.
Autodetachment lifetimes and capture cross-sections
for the associative attachment of electrons by several
groups of organic and inorganic molecules have been measured
and comparisons made with the predictions of the statistical
theory for associative electron capture. Attempts to
calculate electron affinities from this theory, using the
lifetimes and cross -sections measured, met with some
success for simple molecules and enabled conclusions to be
made concerning the adequacy and limitations of the
theoretical treatment.
From studies of the electron energy dependence of
negative ion formation for several groups of inorganic
and organic molecules, various ionisation processes have
been identified. Deconvolution of the ionisation curves
has enabled accurate appearance potential data to be
determined and, in many cases, allowed bond dissociation
energies, electron affinities and heats of formation of
various species to be evaluated
