Qualitative propagator theory of AX4 Auger spectra

Abstract

Nonempirical, parametrized two-electron propagator theory 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 atomic calculations. Two-electron propagators are derived using the superoperator formalism. The working equations yield some popular expressions that have been used in interpreting molecular Auger spectra as special cases. Partitioning technique reveals qualitative factors that govern configuration mixing in the final state. Electron interaction can play a qualitatively dominant role in some of the final states. Some final states display localization of the holes on the same halogen atom, while others place holes on adjacent halogen atoms. This effect is especially pronounced for valence s orbital holes, but it is also observed for A-X bond orbitals and X lone pair orbitals. Trends in electronegativity differences and orbital sizes determine how much final state localization occurs. Propgator theory permits intensity borrowing between configurations leading to richer predicted spectra for the carbon Auger. The importance of using a theory that qualitatively supersedes molecular orbital theory is emphasized.