Some studies of the electronic structure of small molecules and solid metal oxides

A large proportion of this work has been concerned with the study of small molecules by high temperature photoelectron spectroscopy. A description of the experimental techniques relevant to this part of the project is given and problems associated with recording spectra under high temperature conditions are discussed. Those theoretical methods which have been used to assist in spectral assignment and which form the basis of theoretical studies presented in this thesis are described. The HeI photoelectron spectra of the vapour phase oxides NbO and TaO are presented. These spectra have been assigned by recording the electron impact mass spectra of the vapours and by performing Hartree-Fock-Slater calculations on these molecules. A HeI photoelectron spectroscopic study of U, UO and UO2 vapours is described. This work is the first detailed experimental investigation of the electronic structures of the UO and UO2 molecules. Spectral assignment has been achieved with the aid of relativistic HFS calculations. Photoelectron spectra of gas phase metal oxides prepared in-situ by metal plus oxidant reactions have been recorded. Preliminary spectra of NaO and KO are presented and the feasibility of using this technique to study other metal oxides is discussed. A number of chemiionization reactions between metals and oxidants have been investigated using chemielectron spectroscopy and, where possible, mass spectrometry. It is shown how these studies can be used to gain important information on the reaction dynamics and spectroscopic data for the product ions. A theoretical study of the electronic structure of solid state UO2 is reported. The theoretical method used, the molecular cluster method, is described in detail. The calculations show that a large part of the bonding in crystalline UO2 is covalent in nature. The possibility of applying this method to study localized defects in the hyperstoichiometric oxide phase UO2+x is discussed. A recently constructed spectrometer designed for recording multiphoton ionization (MPI) ion-current and MPI photoelectron spectra of short-lived molecules is described. A study of a stable molecule, NO, has been carried out in order to test the new spectrometer and to optimize its performance. Finally, methods are described which enable the harmonic vibrational frequencies of triatomic molecules to be calculated from theoretically-derived pointwise potential energy surfaces. Results from test calculations on a number of molecules are presented. (DX86222)