Angular-resolved autoionization study of CO on Ni(110): Experiment and theory

Angular-resolved autoionization spectra after core-to-bound excitation of CO absorbed on Ni(110) in the (2×{}1)p2mg structure are presented. The experimental autoionization spectra are compared with calculated spectra for the model system Ni-CO by application of the many-body Green's-function technique using self-consistent-field results--molecular orbital--complete neglect of differential overlap one-particle wave functions. In order to supplement the semiempirical approach we furthermore carried out ab initio calculations of the autoionization rates. The angular dependences of the autoionization lines are explicitly calculated. The core-valence-valence Auger spectrum of Ni-CO after C₁ₛ and O₁ₛ excitation has been calculated by the particle-particle Green's-function method with subsequent calculation of the radiationless Auger rates. The combination of the theoretical approaches and the information gained from the angular electron distribution allows one to assign the spectra obtained after core-to-bound and core-to-continuum excitation within the framework of molecular-orbital theory.