Evolution of adsorbate core-hole states after bound and continuum primary excitation: Relaxation versus decay

The core-hole decay in various CO adsorbates with different bonding, i.e., on Cu(100), Ni(111), and K/Ni(111), was studied after primary excitation into several bound and continuum states using soft-x-ray synchrotron radiation. The C and O KLL spectra of adsorbed CO following the resonant excitation 1s{→}2{π} are very similar to normal Auger spectra for all systems studied, whereas the respective primary energies (resonant absorption and x-ray photoemission binding energy) can be different depending on the chemical environment. For a limited range of photon energies, marked changes are observed, particularly in the O KLL spectra. These changes coincide with a peak in the x-ray absorption spectra and are tentatively explained by primary excitation into Rydberglike core-ionized states which interfere with the screening process.