Molecular cluster calculations for the analysis of CO chemisorption on Ni, Pd, Pt and Ir surfaces

Abstract

Abstract Self-consistent Hartree-Fock-Slater molecular cluster calculations for the chemisorption of carbon monoxide on Ni, Pd, Pt and Ir surfaces are presented. The variation of the energy levels with respect to the height of the CO molecule above a particular surface is calculated with the CO molecule linearly bonded to the surface. The calculations are performed using a XCO cluster, where X = (Ni, Pd, Pt, Ir), with the carbon-oxygen distance ( R CO ) equal to the free molecular value. The variation of the energy levels with varying ( R CO ) distances is investigated in more detail for the NiCO cluster. The chemisorption of CO on palladium is also investigated by performing calculations for a Pd 5 CO cluster representing linear bonding to the surface. Relativistic calculations are presented for the IrCO cluster. The relativistic splitting of the chemisorbed 1 π CO level is found to be less than 0.1 eV. The bonding character of the different clusters are investigated through a Mulliken population analysis. Investigations of the bonding and antibonding character for the CO valence levels have also been analyzed by evaluating the derivatives of the molecular eigenvalues with respect to a change in bond distance to the surface and the ( R CO ) distance, respectively. It is found for the valence levels of the chemisorbed CO molecule that the derivatives of the eigenvalues are about five times larger for a change in the carbon-oxygen distance compared with a change in the carbon-metal distance. The energy separation between the 1 π and 4σ peaks of the chemisorbed CO are evaluated and compared with experimental results. Theoretical ionization energies relative to the Fermi energy are calculated for certain bond distances and compared with experimental values.