NO adsorption and dissociation on Co{1010}

Nitric oxide adsorption and dissociation on Co{10 (1) over bar0} have been studied using reflection absorption infrared spectroscopy (RAIRS), low ener gy electron diffraction (LEED) and thermal programmed desorption (TPD). At 100 K, NO is found to absorb molecularly on the Co{10 (1) over bar0} surfac e with an estimated 0.5 ML coverage at saturation. At low coverages, three adsorption sites, on-top, twofold and threefold, are occupied, while from m oderate coverage to saturation, bridge-bonded NO becomes dominant. A sharp c(2 x 4) LEED pattern is observed at saturation, and a corresponding surfac e structure is proposed for the pattern. For all precoverages of NO, dissoc iation is complete on heating the surface, but the temperature at which dis sociation occurs depends critically on NO coverage and on the presence of t he dissociation products. TPD spectra indicate that no species other than N -2 desorbs below 630 K; c(2 x 6) and p(2 x 3) LEED patterns are observed af ter annealing to 600 K, and removal of O adatoms by H-2 shows that these ar e due to N adsorption. A first-order unimolecular reaction mechanism is pro posed for NO dissociation on Co{10 (1) over bar0}, 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. (C) 2000 Elsevier Scien ce B.V. All rights reserved.