On the interpretation of molecular valence Auger spectra

Abstract

The interpretation of molecular valence Auger spectra by means of ab initio computational methods is discussed. As alternatives to self-consistent-field optimizations of the full Auger spectrum, the feasibility of a procedure based on single ionization potentials and of CI calculations using frozen orbitals is tested. Numerical calculations are performed for the CO, N2, NO, and CO2 molecules, which show especially structure-rich Auger spectra. These spectra are analyzed in detail and they are found to contain three nonoverlapping regions of transitions corresponding to final state vacancies in outer–outer, outer–inner, and inner–inner valence orbitals. It is investigated whether this division of the transitions also is relevant with respect to the magnitude of dynamical relaxation errors in the single ionization potential procedure or with respect to the choice of molecular orbital basis in the CI calculations. CI effects are found to be important for intensities and energies of the Auger transitions in the major energy interval of the spectra. These effects are mainly due to near degeneracies between the main double hole states or between these states and configuration states formed by internal–external double excitations. In particular, configuration states involving π–π excitations are found to give important contributions. The one-center intensity model for Auger transitions is evaluated in the case of an open-shell molecule.