Competing mechanisms of molecular hydrogen formation in conditions relevant to the interstellar medium

J. L. Lemaire, G. Vidali, S. Baouche, M. Chehrouri, H. Chaabouni, H. Mokrane

Research output: Contribution to journalArticlepeer-review

44 Scopus citations


The most efficient mechanism of the formation of molecular hydrogen in the current universe is by association of hydrogen atoms on the surface of interstellar dust grains. The details of the processes of its formation and release from the grain are of great importance in the physical and chemical evolution of the space environmentswhere it takes place. Themain puzzle is still the fate of the 4.5 eV released in H2 formation and whether it goes into internal energy (rovibrational excitation), translational kinetic energy, or heating of the grain. The modality of the release of this energy affects the dynamics of the ISM and its evolution toward star formation.We present results of the detection of the rovibrational states of the just-formed H2 as it leaves the surface of a silicate.We find that rovibrationally excited molecules are ejected into the gas phase immediately after formation over a much wider range of grain temperatures than anticipated. Our results can be explained by the presence of twomechanisms ofmolecule formation that operate in partially overlapping ranges of grain temperature. A preliminary analysis of the relative importance of these two mechanisms is given. These unexpected findings, which will be complemented with experiments on the influence of factors such as silicate morphology, should be of great interest to the astrophysics and astrochemistry communities.

Original languageEnglish (US)
Pages (from-to)L156-L160
JournalAstrophysical Journal Letters
Issue number2 PART 2
StatePublished - Dec 20 2010


  • Astrochemistry
  • ISM: atoms
  • ISM: molecules
  • Methods: laboratory
  • Molecular processes

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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