ADSORPTION OF CH3O ON NI(111)

The adsorption of methoxy on Ni(111) is treated using a many-electron embedding theory, modelling the lattice as a 28-atom, three-layer cluster. Ab initio valence orbital configuration interaction (multiple parent) calculations carried out on a local surface region permit an accurate description of bonding at the surface. The 3d orbitals are explicitly used for four Ni atoms in the local surface region. Methoxy binds strongly to the Ni(111) surface at both three-fold and bridge sites with adsorption energies of 90 and 87 kcal/mol and O-surface distances of 1.51 and 1.59 angstrom, respectively. The calculated adsorption energy for methoxy at an atop Ni site is 61 kcal/mol with an O-surface distance of 1.82 angstrom. The methoxy C-O axis is normal to the surface or inclined 5-degrees or 10-degrees from the ''surface normal at three-fold sites and is inclined 20-degrees- from the surface normal at bridge sites. For methoxy adsorbed at three-fold and bridge sites, the calculated C-O stretching frequencies are 1025 and 1010 cm-1, and the CH3O-surface perpendicular stretching frequencies are 495 and 380 cm-1 respectively. The 5a1, 1e and 2e orbitals of adsorbed methoxy are the orbitals principally involved in bonding with the surface. The bonding of methoxy to the nickel surface is characterized as a combination of ionic and covalent bonding with substantial mixing with Ni 3d orbitals. Adsorption studies of CH3O-Ni and CH3O-Ni3 are also reported. Methoxy basis effects and bonding properties of methoxy upon adsorption on Ni are discussed.