Qualitative propagator theory of CH3CN, CH3NC, and CH3CCH Auger spectra

Abstract

A nonempirical two-electron propagator is employed in the characterization of molecular Auger spectra. Based on the Mulliken approximation for many-center Coulomb integrals, the model Hamiltonian requires three parameters for each valence atomic orbital: an exponent for a Slater function, an orbital energy, and an electron–electron repulsion integral. All of these quantities are taken from results of atomic calculations. Certain adjustments of resonance integrals are made to improve agreement with ab initio calculations of orbital energies. Forms of approximate two-electron propagators are discussed, with an emphasis on qualitative factors that assist in interpreting the results. Important orbital energy differences and electron repulsion integrals that govern final state configuration mixing are identified. Intensities for various final states are separated according to the atoms on which the Auger process is initiated for CH3CN, CH3NC, and CH3CCH. Information about local bonding environments is gathered from the calculations, especially spectral features that correspond to sp3 and sp hybridization schemes. Comparisons to the experimental CH3CN spectra are made; the theory helps to interpret the major spectral features. Regularities in the theoretical results are explained in terms of functional group molecular orbitals and electron repulsions.