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  Global Journal of Physical Chemistry. Volume 2, Issue 2 (2011) pp. 189-200
  Review Article Free Article
Formation of molecular hydrogen on bare grains in the interstellar medium (the connection between astronomic and nano-metric scales)
  Jean Louis Lemaire  
LAMAp/LERMA, Observatoire de Paris & Université de Cergy-Pontoise
Observatoire de Meudon, 5 place J. Janssen, 92195 Meudon, France
Pôle Sciences & Techniques, 5 Mail Gay-Lussac, 95000 Pontoise, France

  Large amounts of molecular hydrogen are observed in several locations of the interstellar medium (ISM) in particular in star forming regions. There is no other explanation for the formation of molecular hydrogen in the tenuous ISM than heterogeneous chemistry taking place at the surface of interstellar dust grains. Where are these grains coming from, what are they made of, what kind of morphology and what sizes do they have are questions to which astronomic observations contribute to answer. Laboratory astrophysics simulations are then performed to understand what mechanisms of molecular formation are occurring on the grains in the various phases of the ISM. An example is presented of molecular hydrogen formation in an excited state on a silicate surface. A tentative explanation of the mechanisms involved is proposed. Theoretical calculations modeling the interaction of the atoms with the surface at a nanoscopic level are required to check the assumptions. Today the use of the scanning tunneling microscope allows also direct in situ observations of molecular formation on surfaces.
  Astrochemistry; Atomic and Molecular Processes; Interstellar Medium  

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