Auger spectra of methyl cyanide and related compounds

Abstract

The gas phase, electron excited Auger spectra of CH3CN, C2H2, N2, and CH4 are presented and analyzed. The C(KVV) spectrum of CH3CN, which contains two carbon atoms with different local environments, is shown to be consistent with independent contributions from an acetylenic-like, sp hybridized carbon (the cyanide carbon) and from a methyl-like, sp3 hybridized carbon (the terminal methyl carbon). The cyanide N(KVV) spectrum is shown to be similar in shape to that of N2 but shifted in energy. Analysis of the CH3CN spectrum on a two-hole binding energy scale shows that the Auger process leads to the same set of doubly ionized final states starting from different core–hole sites in the molecule, but with intensities modulated by the polarization of individual molecular orbitals, i.e., the variation of the electron density local to the various atomic sites represented by a particular molecular orbital. In addition, it is shown that the interaction of the two final-state holes resulting from the Auger transition gives rise to shifts of the spectrum towards lower kinetic energies with respect to that predicted for noninteracting holes, and that these shifts vary in magnitude across the Auger feature.