Detailed balance and phonon assisted sticking in adsorption and desorption of H2/Si

Recent experimental results on the desorption of D₂ from Si show practically no translational heating indicating a low barrier for adsorption. This seems to be at variance with the extremely low sticking coefficient found in adsorption experiments indicating a very high barrier. In order to understand this apparent discrepancy we consider a simple model of local lattice relaxation allowing for different barriers in adsorption and desorption processes. After taking the dynamics of this relaxation into account it turns out that detailed balance in principle is valid. In practice, however, it can not be applied for very large energy releases from lattice distortions. Our model predicts very strong phonon assisted sticking.