The interaction between H and CO coadsorbed on Ni{110}

CO adsorption on Ni{110} and on hydrogen precovered Ni{110} surfaces at 180 K has been studied by FT-RAIRS. On a clean Ni{110} surface CO adsorbs at on-top sites upto a coverage of 0.7 ML. At higher coverages the on-top CO band at 2060 cm−1 decreases in intensity with a concomitant increase in a band at 1960 cm−1 which shifts up in frequency. The (2×1)p2mg structure at 1.0 ML CO coverage shows a single band at 1998 cm−1 attributed to CO tilted at bridged sites. FT-RAIRS of CO adsorption on H precovered Ni{110} surfaces shows complex CO site switching within different CO and H coverage regimes. A model is presented involving compression of H into islands of high coverage and both mixed H and CO and unmixed CO islands are formed. CO adsorbs in the unmixed CO islands the same as that on clean Ni{110}. Within the mixed H/CO islands the first layer nickel atoms reconstruct and a new hydrogen desorption state is observed. The CO site switching observed by FT-RAIRS within the various H and CO coverage regimes is discussed in terms of a dominant indirect interaction.