THEORETICAL-STUDY OF THE VALENCE-LEVEL PHOTOEMISSION SPECTRUM OF C2H4ADSORBED ON A NI METAL-SURFACE

In order to investigate the valence-level photoemission spectrum of C2 H4 adsorbed on a Ni metal surface, we calculated the valence-hole spec tral functions of NiC2H4 (pi bonding) using the ab initio third-order algebraic-diagrammatic-construction (ADC(3)) Green-function method usi ng an extended basis set. We obtained an overall good agreement with e xperiment. The changes in the spectral features such as the changes in the separations of the ionization energies from the gas phase to the chemisorbed phase are due to the metal ligand bonding exerted via the charge-transfer excitations and do not arise from the distortion of th e molecule, which occurs upon chemisorption.