We have developed a model for molecular hydrogen formation under astrophysically relevant conditions. This model takes fully into account the presence of both physisorbed and chemisorbed sites on the surface, allows quantum mechanical diffusion as well as thermal hopping for absorbed H atoms, and has been benchmarked versus recent laboratory experiments on H2 formation on silicate surfaces. The results show that H2 formation on grain surfaces is efficient in the interstellar medium up to some 300 K. At low temperatures (≤100 K), H2 formation is governed by the reaction of a physisorbed H with a chemisorbed H. At higher temperatures, H 2 formation proceeds through a reaction between two chemisorbed H atoms. We present simple analytical expressions for H2 formation that can be adopted to a wide variety of surfaces once their surface characteristics have been determined experimentally.
|Journal||The Astrophysical Journal: an international review of astronomy and astronomical physics|
|Issue number||1 II|
|Publication status||Published - 10 Aug 2002|
- Dust, extinction
- ISM: molecules
- Molecular processes