State interference in resonance Auger and x-ray emission

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Abstract
Starting from a scattering-theory formulation, cross sections for Auger and x-ray decay from energetically shifted inner-shell states are derived. Two situations are studied: (i) when there are several close-lying intermediate core-hole states with no vibrational excitations, in which case a state interference effect is identified; and (ii) when there are several close-lying intermediate states with vibrational excitations, in which case a vibronic interference effect is identified. In the latter case, the present formalism is a many-state generalization of the vibrational interference effects derived from the same type of scattering formalism in our previous paper [A. Cesar, H. Ågren, and V. Carravetta, Phys. Rev. A 40, 187 (1989)]. Applications are carried out for spectra of some few-state model systems. It is found that a conventional analysis in terms of discrete noninteracting (noninterfering) states, such as the one-center decomposition model, is only valid when the ratio (R) between energy shift and lifetime is sufficiently large. For states with small R, a more complete theoretical account must be undertaken, including, e.g., the calculation of phases of the respective transition moments. The presented formalism applies to resonance Auger or x-ray emission spectra, to Auger and x-ray emission from core-electron shake-up states, and also, under certain circumstances, to emission from chemically shifted core-hole states.