Valence-shell electron momentum distributions and ionization energy spectra of tetramethylsilane by symmetric noncoplanar (e, 2e) spectroscopy

Abstract

The ionization energy spectra and electron momentum distributions for the valence shell of tetramethylsilane (TMS) were measured using symmetric noncoplanar (e, 2e) spectroscopy. The (e, 2e) ionization energy spectra were found to be in good accord with the literature photoelectron data, except in the inner valence region where inconsistencies in the photoelectron data have been noted. By taking advantage of the different angular dependence (orbital symmetry) of the inner valence (3t 2) −1 and (4a 1) −1 states, improved values for their ionization energies were obtained. The momentum distributions of the valence orbitals were determined by direct angular correlation scans at selected ionization energies. In the outer valence region where close-lying states were observed, the momentum distributions were estimated by deconvolution from a series of ionization energy spectra measured at selected relative azimuthal angles. The experimental distributions were compared with theoretical distributions generated using standard split-valence Gaussian basis sets. Generally good agreement could be found in the momentum distributions for most of the orbitals. The momentum distributions of TMS were compared with those of other silicon compounds including SiF 4 and SiH 4. In accord with earlier (e, 2e) studies on ligand effects, it was found that the methyl group was less electronegative than the fluorine ligand in these silicon compounds.