THEORETICAL-STUDY OF THE VALENCE-LEVEL PHOTOEMISSION SPECTRUM OF C6H6ADSORBED ON NI, PD, AND PT METAL-SURFACES

The valence hole spectral functions of the NiC6H6, PdC6H6, and PtC6H6 model molecules are calculated by the nb initio third-order algebraic- diagrammatic-construction [ADC(3)] Green-function method using an exte nded basis set. The calculation was performed assuming top-site adsorp tion. The theoretical predictions are compared with the experimental a ngle-resolved valence-level photoemission spectra of C6H6 adsorbed on Ni(110) Pd(110), Pd(111), and Pt(111) surfaces. The calculations provi de an overall good agreement with experiment, and confirm the previous experimentally determined assignment of the spectra. A comparison wit h the results for the free C6H6 molecule shows that the many-body effe cts are considerably enhanced by the presence of the metal atom. There is a strong splitting of the Lines and a concomitant intensity redist ribution caused by the metal-ligand pi-pi charge-transfer excitations . The ordering of the ionization levels of the adsorbate is the same a s the one of the free molecule. For C6H6 on a Ni(110) surface the pres ence of the metal-ligand pi-pi charge-transfer satellite of non-negli gible spectral intensity accompanying the 1b(2) ionization process is predicted about 10 eV below the Fermi level, which has not been observ ed so far. The influence of the bending of the H atoms out of the hexa gonal ring plane on the photoemission spectrum is small.