THE ELECTRONIC-STRUCTURE OF THE SURFACE METHOXY SPECIES ON CU(111)

Using model calculations for a CU25OCH3 cluster the bonding interaction between the methoxy species and a Cu{111} surface has been investigated. In agreement with recent photoelectron diffraction measurements, OCH3 is found to adsorb preferentially in the fcc three-fold hollow site with its O-C axis perpendicular to the surface. The corresponding vibrational spectrum - measured with high resolution electron energy loss spectroscopy - is compatible with this bonding geometry. Moreover, on the basis of the known structure, selection rules are used to definitively assign the adsorbate-induced features in the photoemission spectrum. There is good agreement between the measured ionisation potentials and those obtained from the model calculations via Koopmans' theorem. Taken together, the results confirm a bonding picture in which charge transfer of metal electrons fills the 2e orbitals of the adsorbed OCH3 Species, leading to a largely ionic bond.