Molecular hydrogen desorption from amorphous surfaces at low temperature.

We studied the desorption of hydrogen molecules from amorphous silicates of composition (Fe(x)Mg(1 - x))(2)SiO(4) (0 < x < 1) using thermal programmed desorption (TPD). Selected measurements of formation of molecular hydrogen on and desorption from a single crystal olivine sample were done for comparison. The experiments were conducted in conditions as close as technically possible to those found in selected interstellar medium environments, where the formation of molecular hydrogen takes place on dust grains. From molecular desorption data, we derive the energy distribution of binding sites using a direct inversion method. The application of this type of data to the study of elementary processes of migration of atoms and molecules on and ejection from disordered surfaces at low temperature is discussed.