Surface diffusion of solid hydrogen

A number of experiments have shown that hydrogen molecules can migrate on films of solid hydrogen. This was thought to be a diffusive process but recent experimental findings have led others to a different conclusion, so a question remains about the process by which the hydrogen molecules migrate over their own surface. We report new measurements using a hole-burning technique which confirm these recent experiments but we interpret them differently. We have developed a model for the recovery of the hydrogen which accounts for these results and shows that the H-2 does move diffusively. The diffusion is thermally activated and we have determined the diffusion constant, D-0 = 4.03 x 10(-4) +/- 2.5 x 10(-5) m(2) s(-1), and the activation energy, E = 43 +/- 7 K, for hydrogen.