Sticking and thermal desorption of O2 on Ag(001)

The coverage dependence of the sticking coefficient and temperature programmed desorption kinetics for molecular adsorption of oxygen on Ag(001) are investigated both experimentally and theoretically. The nearly exponential decrease of the sticking coefficient as a function of coverage by about five orders of magnitude is explained within a kinetic lattice gas model to be the result of strong nearest- and next-nearest-neighbor repulsions. The latter also shape the desorption spectra which are calculated within the same model under the assumption that fast surface diffusion maintains the adsorbate in quasiequilibrium during desorption. Because the desorption rate is proportional to the sticking coefficient under these conditions,we find a massive decrease of the pre-exponential factor in the Arrhenius parametrization of the rate as a function of coverage which explains the peculiar shape of the desorption spectra. (C) 1997 American Institute of Physics.