Auger spectra of tetrahedral halides and hydridesa)

Abstract

Auger electron spectra are presented for the gas‐phase molecular species CF₄, SiF₄, CCl₄, and SiCl₄ and discussed in terms of the effect of the interaction of the two final‐state holes on the spectral line shapes. The highly polar character of the bonding for this series leads to systematic behavior with respect to this hole–hole interaction, showing rare gas‐like localized halide spectra for SiF₄ and a delocalized component of increasing intensity as we proceed through the series to SiCl₄, CF₄, and CCl₄. The central atom spectra show a composite line shape resulting from the sum of two versions of the same one‐electron final states but with different values of U (the hole–hole interaction energy). The Auger process occurs as a result of the electron density available at the central atom site but, since the one‐electron orbitals are highly polarized towards the halide, the two holes principally appear around the halide sites. With both holes on the same halide site a rather large U results, but with the two holes on separate halide sites one obtains a reduced value of U. The relative intensity of the smaller U component appears to increase as we proceed through the series SiF₄, SiCl₄, CF₄, and CCl₄. This tendency in both the halide spectra and in the central atom spectra depends on the strength of the intersite interaction. The molecular parameter which seems most reasonable to predict this division between localized and delocalized behavior is the ratio of the halide–halide distance to the halide radius. In addition, we demonstrate that for a rather extended series of molecular species the trends in the value of U can be predicted surprisingly well on the basis of an experimental value of U for Ne and the known atomic and molecular dimensions. The implications of this simple predictive capability to other molecular systems is discussed.