An investigation was made, of the initial stages of water adsorption on Rh(111) at 20K, using infra-red reflection absorption spectroscopy. Isolated water molecules and small water clusters were observed in the low-coverage region. Since thermal diffusion was suppressed at 20K, the formation of water clusters at low coverages was controlled by both the coverage and the transient diffusion on the surface. Within a simple random-walk model of the transient diffusion and clustering process, an estimate was made of the mean lateral displacement from the first impact point to the final adsorption site, giving 7.6Å. An incoming water molecule on Rh(111) was trapped within 8 post-collision hops on average.

Transient Diffusion and Cluster Formation of Water Molecules on Rh(111) at 20K. A.Beniya, K.Mukai, Y.Yamashita, J.Yoshinobu: Journal of Chemical Physics, 2007, 126[14], 141102