Core level shake up structures of N₂ adsorbed on nickel surfaces: Cluster models

Self-consistent Hartee-Fock-LCAO calculations on a linear NiN2 cluster are used to explain the two-peak structure observed in core level photoemission from N2 adsorbed on the Ni (100) surface. The two observed peaks are due to different N2 core hole final states, a screened and an unscreened final state that can be clearly identified in the cluster model. The energy separation and intensity ratio (computed using the sudden approximation) of the two final states in NiN2 are comparable with the experimental peak separation and intensity ratio for reasonable cluster geometries. A comparison with previous model studies on NiCO is used to explain the different shape of the core level spectra of N2 and CO adsorbed on nickel surfaces. © 1981.