The interaction of H atoms with interstellar dust particles: Models

Two topics of relevance for 112 formation in the, interstellar medium are considered: (i) the interaction of H and H-H with a model-graphite surface (Coronene: C24H12), and (ii) H- formation by charge transfer in the interaction of H with a model-silicate surface (MgO{100} representing forsterite: Mg2SiO4{100}). The first topic is related to the frequently invoked Langmuir-Hinshelwood and Eley-Rideal mechanisms for H-2 formation near carbonaceous zones of interstellar dust grains. Ab initio calculations based on Density Functional Theory are used. The second topic proposes a new scenario in which the efficient production of H- ions would subsequently enable the formation of H-2 via associative detachment. It stems from recent work of the authors on charge transfer between neutral atoms and ionic insulators.