Open Collections

Molecular inner-shell excitation studied by electron impact

University of British Columbia

Electron impact and electron spectroscopic techniques provide many useful tools for the examination of the physical structure of matter. One of these tools is electron energy loss spectroscopy (EELS). This thesis describes the application of EELS to studies of excitations of the inner-shell electrons of gaseous molecules. Preliminary, low resolution studies in the Department of Chemistry at UBC by G.B. Wight have demonstrated that the technique is experimentally feasible and that many interesting spectroscopic features occur in the inner-shell electron energy loss spectra (ISEELS) of molecules. The present work builds on this foundation and has provided significant extensions not only of the technique but also of its application. Improvements in the experimental apparatus have led to higher energy resolution and more flexible scanning arrangements. The molecular I SEE L spectra of several series of related molecules have been studied including investigations of all observable inner-shell excitation structure between 50 and 700 eV in the simplest saturated, unsaturated and aromatic hydrocarbons (CH₄, C₂H₆, C₂H₂, C₂H₂ and C₆H₆), the methyl halides (CH₃X, X = F, Cl, Br, I), the monohalobenzenes (C₆H₅X, X = F, Cl, Br, I), the chloromethanes (CHxCl₄-x, x = 0 to 4) and chloroethane. A number of specific investigations have been carried out in order to assist spectral interpretations and to further understand the physical nature of inner-shell excitation phenomena. Isotopic substitution has been used to aid the assignment of the carbon 1s spectra of CH₄ (CD₄) and CH₃Br (CD3Br). The first observation of the gas phase energy loss equivalent of extended X-ray absorption fine structure (EXAFS) is reported in the spectra of CH₂CI₂, CHCI₃ and CCI₄. Molecular electric quadrupole transitions have been identified in the sulphur 2p excitation spectrum of SF₆. The improved experimental resolution has led to observations of vibrational structure in the inner-shell excitation spectra of N₂, CO, C₂H₄ and the methyl halides. In addition to the ISEELS studies, electron-ion coincidence techniques have been used to study the ionic fragmentation following excitation and ionization of a sulphur 2p electron in SF₆. This experiment was performed at the FOM Institute for Atomic and Molecular Physics in Amsterdam. An attempt has been made to evaluate alternate theoretical descriptions of certain characteristic inner-shell excitation features in the light of both the electron-ion coincidence results and ISEELS studies of the chloromethanes and SF₆.

Text

2010-03-02

For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.

http://hdl.handle.net/2429/21327

Chemistry

University of British Columbia

Graduate