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Title: Studies in photoionisation
Author: Maier, John Paul
ISNI:       0000 0001 3616 8874
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 1972
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The studies in photoionisation in molecules presented in this thesis were accomplished by the technique of Photoelectron Spectroscopy. The gaseous molecules are irradiated by photons of discreet energy (hν), sufficient to eject electrons, and through the analysis of the kinetic energies (En) of the photoelectrons the ionisation energies (In) can be determined from Einstein's photoelectric equation En = hν - In Ionisation phenomena and the means of relating the information to electronic structure and dimensional changes are discussed. The techniques used to study electronic processes in the vacuum ultra-violet are outlined and the advantages, limitations in the experimental aspects and interpretation of data compared. The features of significance in photoelectron spectroscopy are discussed both from the theoretical and experimental viewpoint. The instrumental development since the initial work in the early sixties is reviewed and the experimental criteria outlined. The modifications carried out in conjunction with this work and the experimental details are presented. In the lowest ionisation process in phosphine and phosphorous trifluoride an extensive vibrational progression is discernible. The sufficiently high quality data allows a detailed discussion of the geometry of these ions, barriers to inversion and potential functions. The analysis suggests that the ground ionic state of phosphorous trifluoride is very probably strictly planar, while that of phosphine is pyramidal with a very small barrier to inversion. The higher ionisation energies are discussed in view of-the spectral detail and a molecular orbital scheme. In the study of steric inhibition of resonance in substituted benzenes, it is shown that through the correlation of Π-energy levels in series of related molecules, electronic and steric effects can be separated and the relative importance of the latter estimated. In biphenyls an empirical correlation between certain bands in the spectra and dihedral angle is.noted and its use in conformational studies emphasised. The variation of the photoelectron Π-ionisation energies in biphenyls, phenyl ethylenes, anilines, phenols and related molecules is rationalised on a semi-quantitative basis by a Hückel-type theory based on the interaction of semi-localised Π-MOs. The dihedral angles in sterically hindered, or rigidly held, phenyl ethylenes and anilines can then be inferred. The validity of the semi-empirical treatment is demonstrated by the success in reproducing the photoelectron data. Discussion of the Franck-Condon envelopes gives support to the assignment of the Π-MOs, indicating geometrical changes. In the anilines the deduction is that nitrogen is non-planar. Features of interest in the individual molecules are also discussed. Correlation diagrams are used extensively to illustrate the trends, choice of basis set parameters, and to summarise the assignments.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available