Line shapes in resonant photoemission spectra

Abstract

Photoemission involving an intermediate core-hole \ensuremath{\rightarrow} bound-valence transition shows a strong resonance enhancement as the photon energy is tuned through the intermediate-state transition energy. We have studied the effects of electronic relaxation in both intermediate and final states on the line shapes of this resonant photoemission spectra. We consider two simple models of the relaxation process---discrete plasmon-type relaxation and continuous electron-hole-pair relaxation models---and calculate the photoemission cross section as a function of both final photoelectron energy $\ensuremath{\epsilon}$ and incident photon energy $\ensuremath{\omega}$. In the case of discrete plasmon-type relaxation, $\ensuremath{\omega}$ dependence of the plasmon satellite strength shows qualitative differences depending on the plasmon coupling constants in the intermediate and final states. If a damping or dispersion of plasmons is included, there appears a new peak at fixed electron kinetic energy in addition to the usual plasmon satellite which we call a fluorescent electron emission peak, as a result of intermediate-state relaxation. In the continuous electron-hole-pair case, the Doniach-Sunjic asymmetry parameter depends on the incident photon energy $\ensuremath{\omega}$. This $\ensuremath{\omega}$ dependence arises because the system has a longer time to adjust towards the fully relaxed intermediate state when the system is on resonance, while the final-state relaxation determines the line shape off resonance.