Multichannel scattering theory of the resonant Auger effect in photoelectron spectroscopy

Abstract

Photoelectron spectroscopy has allowed us recently to observe both giant resonance enhancement of primary lines and two-electron resonant Auger satellites corresponding to the resonant behavior of photoemission cross sections relative, respectively, to autoionization and Auger decay channels. Using multichannel scattering theory and configuration-interaction formalism, I have established general formulas to parametrize the photoemission cross sections in the neighborhood of nonradiatively decaying excited states located near inner-shell ionization thresholds. Considering both cases of one isolated resonance and $n$-resonant states decaying into $N$ continua, I have shown why the two types of decay (autoionization and Auger) cannot be treated independently and have stressed the importance of coupling autoionization channels with Auger ones to account for the asymmetry profile of Auger partial cross sections and the presence of extra structures due to neighboring resonances in Auger channels. Some examples are discussed to point out that the relative importance of primary and satellite lines may vary strongly with the element and the energy range considered. The determination of the parameter ${\ensuremath{\alpha}}_{n}(\ensuremath{\mu}E)$ typical of a resonance $n$ in each channel $\ensuremath{\mu}$ provides us with many types of information, such as the importance of interchannel coupling, spin-orbit effects, and the existence of shake-up satellites.