Date of Award
Doctor of Philosophy (PhD)
Professor Adam P. Hitchcock
In contrast to photoabsorption techniques, which are subject to electric dipole selection rules, electron energy loss spectroscopy (EELS) can provide a more complete investigation of atomic and molecular electronic structure. This is due to the added capability of accessing dipole and/or spin forbidden electronic transitions under conditions of significant momentum transfer.
This work documents the design, construction and performance of a new, high resolution, variable scattering angle, variable impact energy electron spectrometer (McVAHRES) which has been used to investigate electronic transitions in gas phase atoms and molecules under both dipole and non-dipole conditions. The home-built instrument features a complex electron optics system and a sophisticated, computer-interfaced electronics system which allows a high degree of flexibility with regards to control and acquisition. This permits a wide range of experimental conditions.
New spectroscopic studies include the observation of spin-forbidden, C is core excited triplet states in C₂H₄, C₂H₂, and C₆H₆. The momentum transfer dependence of the (C 1sˉ¹, π*) ³π state of CO was also investigated. These results are compared to the results of theoretical calculations. Generalised Oscillator Strengths (GOS) as a function of momentum transfer were derived for the S 2p edge of SF6. This work greatly expands previous results reported in the literature. Finally, an interesting feature was observed in the S 2p spectrum of SF₆, which displays quadrupolar momentum transfer behaviour.
Francis, James T., "Non-Dipole and Dipole Core Electronic Excitation" (1995). Open Access Dissertations and Theses. Paper 1778.