Energetics of H2 Formation on Astrophysically Relevant Surfaces

The surface recombination of H atoms releases approximately 4.5 eV of energy, which may be distributed between the solid, the desorption of the newly formed H molecule and the translation, vibrational, and rotational degrees of freedom of the desorbed molecule. Computational studies by Takahashi and Uehara (2001) and Duley and Williams (1993), among others, suggest that formation pumping of excited H may be observable in diffuse or dark clouds, and that it can be differentiated from UV pumping and be surface specific. In this paper we present our experimental apparatus designed to perform the first laboratory measurements of the energy distribution of H₂ molecules forming on astrophysically relevant surfaces.