Absorption spectra of silyl compounds in the vacuum ultra-violet

Abstract

The electronic absorption spectra of disilyl ether, hexamethyl disilyl ether, silyl chloride, trisilyl amine and disilyl methyl amine have been obtained. The spectra occur in the vacuum ultra-violet and, with the exception of a few diffuse bands in the spectrum of silyl chloride, are all continuous. Comparisons of the positions of the absorption maxima, however, with the spectra of the corresponding methyl compounds show that the spectrum of each silyl compound studied is shifted to the violet relative to the spectrum of the corresponding methyl compound. The shifts are large, being one-half to several eV, and strongly suggest that the first ionization potential of each silyl compound used is considerably greater than that of the corresponding methyl compound. The ionization potential increases can be qualitatively explained in terms of loss of non-bonding, “lone-pair”, character and gain of bonding character, of certain orbitals on passing from the carbon to the silicon compounds, which loss and gain may be consequent upon the possession by a Si atom, but not by a C atom, of valency shell d orbitals.