Theory of resonant photoemission of adsorbates on metal surfaces

Abstract

Elementary processes of a resonant valence photoemission are studied for adsorbates on metal surfaces whose initial configuration consists of the occupied core, valence levels and unoccupied level, below and above the Fermi level of a metal, respectively. The radiative excitation of the core electron is followed by several decay channels including the Auger process in which a valence electron fills the core-hole and another valence electron is emitted as a photoelectron. When the core electron is resonantly excited into the adsorbate unoccupied level and remains there as a spectator, the resulting final state can be viewed as either a modified Auger or shake-up state of the photoemission process in the sense that the final state has two holes in the valence levels and one electron in the initially empty level. The characteristic features of the valence photoelectron spectra following resonant core excitation are calculated by using a perturbation formula for the second order optical process. It is shown that the relaxation processes towards various valence final states are crucially dependent on the residence time scale of the excited electron in a highly localized state relative to the core-hole life time.