Photoelectron Spectra and Bonding in Some Halosilanes

Abstract

The photoelectron spectra of some halosilanes, SiH3X (X = F, Cl, Br), SiH2X2 (X = F, Cl), and SiHCl3 have been studied, to obtain information on the bonding, especially (p → d)π back-bonding to silicon. The spectra were assigned on simple orbital overlap grounds, by comparison with the carbon analogues and by use of CNDO/2 calculations. Few discrepancies were found, but in these cases the first method was preferred. There is ample evidence from the individual ionization potentials and by comparison of the spectra with those of the analogous carbon compounds for interaction of the halogen pπ electrons with the silicon d orbitals. This is also indicated by some empirical calculations on the chlorosilanes, which also confirm the assignment of the spectra.It can also be shown that the ionization potentials are consistent with the silicon–halogen σ bond strength decreasing through the series H3SiF > H3SiCl > H3SiBr.