Photoelectron spectra (hv = 21.22 eV) and thermal desorption data were obtained for CO and H coadsorbed on W(100) at 80 K. When the clean surface is exposed to a saturation dose of H2, subsequent exposure to CO results in the formation of a state whose emission spectrum is similar to that of molecular -CO. Upon heating to ~280 K, a structural rearrangement occurs in which most of the adsorbed CO is converted to the strongly bound form as the hydrogen is simultaneously desorbed. These data plus the observation that H2 cannot be adsorbed to any significant degree on a saturated layer of -CO suggest that adsorbed -CO and H occupy the same atomic sites on the W(100) surface. The distinction between long and short range repulsive CO---H interactions is discussed. For CO adsorbed on clean W(100), the range of activation energies for vigin to conversion is calculated from the UPS data to be 45-62 kJ/mol.
Citation: Surface Science
Pub Type: Journals