High-resolution Core-level Spectroscopies Of Molecular Silicon Compounds Using Monochromatized Synchrotron Radiation

High-resolution core-level photoabsorption, photoelectron and photoionization mass spectra of numerous substituted silane molecules have been measured in the gas phase around the Si 2p ionization edges using monochromatized synchrotron radiation. Photoabsorption spectra were also measured around the Si 2s ionization edges and the Cl 2p ionization edges of the chlorine-containing molecules. Multiple-scattering X{dollar}\alpha{dollar} calculations were performed to aid in the assignment of the peaks observed in the photoabsorption spectra. The chemical series approach, where the effects of small systematic chemical changes in the composition of the molecule under study on the observed spectra provide useful aids for assignments, has been used throughout this work.;Photoabsorption spectra of the core electronic levels are reported for three series of silicon molecules, the fluoromethylsilane compounds: Si(CH{dollar}\sb3{dollar}){dollar}\sb{lcub}\rm x{rcub}{dollar}F{dollar}\sb{lcub}\rm 4-x{rcub}{dollar}, the chloromethylsilane compounds: Si(CH{dollar}\sb3{dollar}){dollar}\sb{lcub}\rm x{rcub}{dollar}Cl{dollar}\sb{lcub}\rm 4-x{rcub}{dollar}, and the chlorosilane compounds: SiH{dollar}\sb{lcub}\rm x{rcub}{dollar}Cl{dollar}\sb{lcub}\rm 4-x{rcub}{dollar}, x = 0-4. Theoretical results from MS-X{dollar}\alpha{dollar} calculations along with trends observed in the experimental spectra facilitate the identification and assignment of numerous features in the spectra. Below the ionization edges, the observed peaks are assigned to result from electronic transitions of the core electrons into virtual molecular orbitals and Rydberg orbitals. Above the ionization edges, peaks in the photoabsorption cross sections are assigned to transitions into a variety of quasibound states in the continuum: virtual molecular orbitals and Rydberg orbitals. Above the ionization edges, peaks in the photoabsorption cross sections are assigned to transitions into a variety of quasibound states in the continuum: virtual molecular orbitals supported by the shape of the molecular potential, shape resonances, and delayed-onsets resulting from centrifugal barriers to the exiting electron.;Using a newly constructed photoelectron spectrometer, Si 2p photoelectron spectra of eleven substituted silane molecules were measured with unprecedented experimental resolution. The spectra exhibit vibrational broadening, and for silane, tetrafluorosilane and ethylsilane, individual vibrational bands are resolved on the Si 2p photoelectron lines. Very high experimental resolution is required to resolve individual vibrational bands. Extensive use is made of the equivalent-cores approximation to aid in the interpretation of the observed vibrational structure. Chemical effects on the lifetimes of the Si 2p core holes are also investigated. Total ion yield spectra, total electron yield spectra, photoionized mass spectra and mass-resolved photoion yield spectra of the fluoromethylsilane compounds, Si(CH{dollar}\sb3{dollar}){dollar}\sb{lcub}\rm x{rcub}{dollar}F{dollar}\sb{lcub}\rm 4-x{rcub}{dollar}; x = 0-4, measured using photon energies around the Si 2p core ionization edges are also reported. In the fragmentation patterns observed following irradiation of the sample with monochromatized synchrotron radiation, the methyl groups are found to be more labile than the fluorine atoms at photon energies below and above the Si 2p ionization edges. Partial ion yields of the SiF{dollar}\sp-{dollar} and SiMe{dollar}\sp+{dollar} fragment ions are seen to exhibit specific enhancement at the Si 2{dollar}p\to\sigma{dollar}* resonances below the ionization edge