A static SIMS study of the chemisorption of CO on Ni(111)

SIMS spectra were obtained for CO adsorbed on Ni(100) at 300 K and on Ni(111) at 300 and 185 K. Changes in ion yield ratios with CO coverage are shown to correlate with various surface structures observed by LEED and vibrational spectroscopy. For example, there is a dramatic decrease in the NiCO⁺/Ni⁺ ratio for CO on Ni(111) at 185 K at exposures corresponding to the coverage where CO molecules shift from threefold to twofold bridged sites and where the onset of the ( 3× 3)R30° LEED structure is observed. It is suggested that cluster formation is a very complex process. Thus it is not possible to make simple correlations between Ni₂CO⁺ and bridge-bonded CO and NiCO⁺ and linear bonded CO, even though the yields of these species are influenced by the surface structure.