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Astron. Astrophys. 334, 363-375 (1998)

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Molecular dynamics simulation of the H2 recombination on a graphite surface

P. Parneix and Ph. Bréchignac

Laboratoire de Photophysique Moléculaire1 , C.N.R.S. Bât 210, Université de Paris-Sud, F-91405 Orsay Cedex, France (philippe.brechignac@ppm.u-psud.fr)

Received 4 August 1997 / Accepted 22 January 1998


This article reports a model study aimed at the detailed description of the mechanism of formation of molecular hydrogen onto dust grain surfaces in the interstellar medium. Using classical trajectories (CT) and quasi-classical trajectories (QCT) calculations, the H2 recombination from the Eley-Rideal process has been studied. This reactive process, involving the collision between one gas phase atomic hydrogen and one other H atom previously chemisorbed on a graphite surface, could be an efficient mechanism to explain the formation of H2 in the interstellar medium. Two empirical potential models have been used to extract the main physical and chemical properties of this system. The efficiency of the recombination process has been analysed as a function of the collision energy and also as a function of the H coverage on the graphite surface. From an energetic point of view, the newly formed H2 molecules have been found to be desorbed with a large translation kinetic energy and also in highly excited vibrational states.

Key words: dust, extinction – ISM: molecules – molecular processes

© European Southern Observatory (ESO) 1998

Online publication: May 12, 1998