The diffusion and interactions of CO molecules on Pd(111) were studied by scanning tunnelling microscopy. By following the random walk motion of individual molecules as a function of temperature, an activation energy barrier for diffusion of 118meV was determined. The interaction between CO molecules was found to be repulsive for pairs separated by one or two Pd(111) lattice distances, and weakly attractive at a separation of √3.

Diffusion and Pair Interactions of CO Molecules on Pd(111). T.Mitsui, M.K.Rose, E.Fomin, D.F.Ogletree, M.Salmeron: Physical Review Letters, 2005, 94[3], 036101 (3pp)