Multielectron excitations in high-energy photoelectron spectra of CO adsorbed on Ni(100)

High-resolution x-ray-excited core-level shake-up and valence-electron spectra of CO adsorbed on Ni(100) in the c(2×{}2) structure are presented. A number of newly resolved structures are reported. The C 1s and O 1s shake-up spectra show pronounced differences. The shake-up transitions are treated as local molecular excitations in the presence of the core hole. It is proposed that transitions from the 2π* screening orbital into 3p and other higher states with Rydberg character give rise to the most intense shake-up peaks in adsorbed CO. In the C 1s spectrum a low-energy satellite is identified as an excitation from bonding to antibonding 2π*-3d combinations. The high-energy shake-off continua reveal several broad structures which are interpreted as autoionizing or shape resonances in the shake-off continua. These features are compared with thresholds observed in photon-stimulated-ion-desorption spectra for adsorbed CO. The difference spectrum between the valence region of Ni with and without adsorbed CO reveals several features over an energy range of 40 eV. The 3{σ} state and the correlation satellites are compared with features in the autoionizing spectra at the core-level thresholds.