The diffusion coefficients were deduced from a coverage profile analysis of photo-emission electron microscopic images. The diffusion coefficients of CO and O on a (110) surface were obtained for 318 to 438K and 606 to 668K, respectively. The diffusivity of CO did not exhibit a marked dependence upon the surface coverage, but was appreciably dependent upon surface reconstruction. The anisotropy of diffusion was of the order of a factor of 2. On the other hand, O exhibited anisotropy; with diffusion occurring essentially only parallel to the [110] direction. It also exhibited a marked coverage dependence. At an O coverage of less than 0.2 of a monolayer, the diffusion coefficient was larger (by an order of magnitude), than at high coverages. The activation energies for

CO diffusion were between 9 and 13kcal/mol, while O required an activation energy of 30kcal/mol at low coverages and of 40kcal/mol at high coverages.

A.Von Oertzen, H.H.Rotermund, S.Nettesheim: Surface Science, 1994, 311[3], 322-30

Table 242

Diffusion of NO on (111)Pt Surfaces