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UBC Theses and Dissertations

Absolute molecular electronic spectroscopy at UV and soft X-Ray energies by hihg-energy electron impact Burton, Gordon R.

Abstract

Dipole (e,e) spectroscopy has been used to determine absolute photoabsorption oscillator strengths (cross sections) for electronic excitation of CC14, CH3OH, NH3, CH3NH2, (CH3)2NH, and (CH3)3N at energy resolutions in the range 0.048-1.0 eV fwhm. These data have been obtained in the valence, and inner shells (Cl 2p,2s; C is (CC14), and C is (CH3OH)), spanning the visible to soft X-ray equivalent photon energy regions(5.0-400 eV). Absolute scales have been established using the Thomas-Reiche-Kuhn sum rule. Dipole (e,e+ion) spectroscopy has been employed to study the molecular and dissociative photoionization in the valence shell of CH3OH, and in the valence and inner shells of CC14. Time-of-flight mass spectroscopy is used to determine photoionization branching ratios and photoionization efficiencies. These data are combined with the corresponding absolute photoabsorption oscillator strength data, to determine the partial oscillator strengths for the molecular and dissociative photoionization channels of these molecules. In addition, the measurements have been used to provide detailed quantitative information on the breakdown pathways of these molecules following the absorption of energetic radiation. The absolute photoabsorption measurements for ammonia and the methylamines have been used in a collaborative research project with Professor W.J. Meath, involving theoretical work at the University of Western Ontario. The results provide accurate values for many of the dipole properties of these nitrogen-containing molecules, as well as integrated dipole oscillator strength distributions for the entire photo absorption spectrum. In other work, a new high impact energy electron energy-loss spectrometer of high sensitivity has been designed and constructed. This instrument features an open scattering region, high incident electron beam energy, and multichannel detection, in order to measure absolute photo absorption oscillator strength data for not only stable atoms and molecules, but also for low-density targets including free radicals, ions, and laser-excited species.

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