The surface geometry of carbonmonoxide and hydrogen co-adsorbed on Ni{1 1 1}

Abstract A combination of photoelectron spectroscopy, temperature programmed desorption and low energy electron diffraction structure determinations have been applied to study the p(2 × 2) structures of pure hydrogen and co-adsorbed hydrogen and CO on Ni{1 1 1}. In agreement with earlier work atomic hydrogen is found to adsorb on fcc and hcp sites in the pure layer with H–Ni bond lengths of 1.74 A. The substrate interlayer distances, d 12  = 2.05 A and d 23  = 2.06 A, are expanded with respect to clean Ni{1 1 1} with buckling of 0.04 A in the first layer. In the co-adsorbed phase CO occupies hcp sites and only the hydrogen atoms on fcc sites remain on the surface. d 12 is even further expanded to 2.08 A with buckling in the first and second layer of 0.06 and 0.02 A, respectively. The C–O, C–Ni, and H–Ni bond lengths are within the range of values also found for the pure adsorbates.