Competition between relaxation and decay of a resonantly excited core-hole state

By a many-body theory it is shown that in general when the time scale of the relaxation from the resonantly excited core-hole state to the fully relaxed core-hole state is much shorter than that of core-hole decay, the autoionization (deexcitation) spectrum is more or less identical to the Auger-electron spectrum by core-hole decay of the fully relaxed core-hole state. Here, the fully relaxed core-hole state is the lowest core-hole state in the X-ray photoelectron spectroscopy spectrum. The present theory explains why the C 1s autoionization spectrum of CO molecule adsorbed on Ni(1 0 0) surface measured at the resonant core-level electron excitation energy is more or less indentical to the Auger-electron spectrum measured at far above the core-level electron ionization limit.