Reaction of chemisorbed CH and H on nickel

Abstract

The reaction of chemisorbed CH and H on the [111] surface of Ni is treated using a many-electron embedding theory to describe the electronic bonding, modelling the lattice as a 28-atom, three layer cluster. Ab initio valence orbital CI calculations carried out on a local surface region permit an accurate description of bonding at the surface. Both CH and CH2 species are found to bind strongly to the Ni(111) surface at threefold and bridge sites. Adsorption energies are between 2.9 and 3.1 eV for CH adsorption, and 2.5 and 2.9 eV for CH2 adsorption. Atop Ni adsorption sites are more than 1 eV higher in energy. The Ni–C bond lengths range from 2.00 to 2.04 Å for CH and CH2 on the surface. Vibrational frequencies for HC-surface and H2C-surface vibrations are between 400 and 600 cm−1; CH stretching frequencies are around 3050 cm−1 in both CH and CH2. The reaction of CH+H→CH2 on the nickel surface is 1.45 eV exothermic, however, a barrier exists to moving H to a threefold site adjacent to one occupied by CH. The geometries of CH and CH2 and the nature of the bonding to the surface are discussed.