Are molecule-covered dust grains efficient catalysts of H 2 formation in the cold ISM?

L. Gavilan, J. L. Lemaire, Gianfranco Vidali

Research output: Contribution to journalArticle

12 Scopus citations

Abstract

The formation of H 2 in the interstellar medium (ISM) involves complex processes, some of which are still not understood. In cold regions, it is assumed that H 2 formation follows Langmuir kinetics, i.e. the immediate desorption of incoming atoms or molecules on a surface already saturated with molecules. Our experiments address this issue by studying the formation of H 2 on a dust surface dosed with molecules prior to atomic exposure. We simulate ISM conditions at T dust < 10K and T gas ~ 90K and use a synthesized amorphous silicate. By coupling laser detection to thermal desorption spectroscopy, we confirm that hydrogen recombination is promptly enhanced. We interpret this as a result of enhanced atomic diffusion (both hopping thermal and quantum mechanical tunnelling). Moreover, since H 2 formation is the most exothermic chemical reaction per unit mass, we elucidate its importance as a non-thermal desorption mechanism. We apply these results to dense ISM regions where H 2 formation and its induced desorption are curbed by a declining atomic gas-phase abundance. We further propose this as a pathway to deuterium fractionation in pre-stellar cores. More importantly, we show that dust remains an active catalyst even in the coldest ISM.

Original languageEnglish (US)
Pages (from-to)2961-2970
Number of pages10
JournalMonthly Notices of the Royal Astronomical Society
Volume424
Issue number4
DOIs
StatePublished - Aug 21 2012

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Keywords

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

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

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