UBC Theses and Dissertations

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UBC Theses and Dissertations

The photoionization and dissociation of molecules Mak, Danny Shiu Hung


The present work is concerned with photoionization efficiencies of gases and vapors determined as a function of photon energy by vacuum spectroscopy and mass analysis. The photoionization work was performed to obtain fundamental information about some simple molecules, and it was hoped that the results would provide a means to explain the apparent discrepancies of threshold ionization potentials previously reported by other workers. Results on the photoionization of sixteen atoms and molecules, namely: argon, krypton, xenon, oxygen, nitrogen, carbon monoxide, chlorine, hydrogen chloride, ammonia, water, methane, methane-d₄, propylene, acetylene, methyl cyanide and methyl alcohol for the energy range from eight to twenty-one electron volts are presented. Photoionization efficiency curves of these molecules were obtained from which numerical values of ionization potentials, dissociative-ionization appearance potentials and dissociation energies are deduced, and the fine structure and autoionization processes are interpreted. The results are discussed and compared with those obtained by other investigators. The threshold and inner ionization potentials of these molecules are in close agreement with spectroscopic values and are superior to those obtained by the electron impact method. A brief account of the historical developments leading to the present work is described, and a few existing methods for the determination of ionization potentials with their advantages and limitations are pointed out. The essential components of the instrument and their special characteristics are briefly discussed, and the major sources of error are also included. The limitations of the apparatus at the present stage are pointed out, and improvements are suggested. The reasons for the choice of molecules for this work is mentioned, and an outline for further work is also suggested.

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