NO adsorption and dissociation on Co{1010}

Nitric oxide adsorption and dissociation on Co{101̄0} have been studied using reflection absorption infrared spectroscopy (RAIRS), low energy electron diffraction (LEED) and thermal programmed desorption (TPD). At 100 K, NO is found to absorb molecularly on the Co{101̄0} surface with an estimated 0.5 ML coverage at saturation. At low coverages, three adsorption sites, on-top, twofold and threefold, are occupied, while from moderate coverage to saturation, bridge-bonded NO becomes dominant. A sharp c(2×4) LEED pattern is observed at saturation, and a corresponding surface structure is proposed for the pattern. For all precoverages of NO, dissociation is complete on heating the surface, but the temperature at which dissociation occurs depends critically on NO coverage and on the presence of the dissociation products. TPD spectra indicate that no species other than N2 desorbs below 630 K; c(2×6) and p(2×3) LEED patterns are observed after annealing to 600 K, and removal of O adatoms by H2 shows that these are due to N adsorption. A first-order unimolecular reaction mechanism is proposed for NO dissociation on Co{101̄0}, with a strong dependence of the activation energy for surface dissociation on both NO coverage and the coverage of the dissociation products, N and O.