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    Formation of H₂ in the interstellar medium at high temperature
    (2011-11-22) Iqbal, Wasim; Acharyya, Kinsuk; Herbst, Eric
    We used the continuous-time random-walk (CTRW) monte carlo technique to study the formation of H₂ on the surface of interstellar dust grains with both physisorption and chemisorption sites on olivin and carbonaceous material. we have considered hydrogen atom mobility due to both thermal hopping and quantum mechanical tunneling. In addition, we have also considered rough surfaces with multiple binding sites . Tunneling is found to dominate the surface chemistry at low temperature, but as the temperature increases, the scenario changes. The inclusion of chemisorption sites can provide a meaningful efficiency for H₂ production up to as high a temperature as 700 K depending upon the depth of the chemisorption well. We found that over virtually the entire temperature range studids, the use of rate equations overestimates the H₂ formation rate. This overestimate is large at high temperatures, due to very low surface residence times.