Wetting transitions of hydrogen and deuterium on the surface of alkali metals

Although wetting transitions have been observed for helium and hydrogen on alkali metal surfaces, no finite temperature, quantum simulation studies of these systems have been able to conclusively locate a wetting transition. This paper presents such calculations for the systems H₂ and D₂ on Rb and Cs, using semiempirical hydrogen-hydrogen interactions and ab initio gas-surface interactions. Comparison with experiment implies that the adsorption potential is ~10% more attractive than is predicted by current theory. Simulations of H₂ adsorbing on a 15 {} thick film of Rb on Au predict that this system will show a decrease in the wetting temperature of about 1 K compared with H₂ on pure Rb. The simulations reveal that a commonly used ``simple model'' is surprisingly accurate.