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

The translational energy of D₂ desorbed from Si(100) and Si(111) surfaces was measured and found roughly equal to the thermal expectation at the surface temperature Tₛ. Combining these results with previously measured internal state distributions, the total energy of the desorbed molecules is approximately equal to the equilibrium expectation at Tₛ. 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.