Hydrogen adsorption on and desorption from Si: Considerations on the applicability of detailed balance

The translational energy of ${\mathrm{D}}_2$ desorbed from Si(100) and Si(111) surfaces was measured and found roughly equal to the thermal expectation at the surface temperature ${\mathit{T}}_{\mathit{s}}$. Combining these results with previously measured internal state distributions, the total energy of the desorbed molecules is approximately equal to the equilibrium expectation at ${\mathit{T}}_{\mathit{s}}$. Thus adsorption experiments, which suggest a large energetic barrier, are at variance with desorption experiments, which exhibit a trivial adsorption barrier, and the applicability of detailed balance for this system needs to be reexamined.