Are molecule-covered dust grains efficient catalysts of H2 formation in the cold ISM?
| Autor: | Jean-Louis Lemaire, Gianfranco Vidali, Lisseth Gavilan |
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| Rok vydání: | 2012 |
| Předmět: |
Physics
Astrochemistry Hydrogen Thermal desorption spectroscopy chemistry.chemical_element Astronomy and Astrophysics 010402 general chemistry 01 natural sciences Chemical reaction 0104 chemical sciences Atomic diffusion Deuterium chemistry 13. Climate action Space and Planetary Science Chemical physics Desorption 0103 physical sciences Molecule Atomic physics 010303 astronomy & astrophysics |
| Zdroj: | Monthly Notices of the Royal Astronomical Society. 424:2961-2970 |
| ISSN: | 0035-8711 |
| Popis: | The formation of H2 in the interstellar medium (ISM) involves complex processes, some of which are still not understood. In cold regions, it is assumed that H2 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 H2 on a dust surface dosed with molecules prior to atomic exposure. We simulate ISM conditions at Tdust < 10 K and Tgas ∼ 90 K 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 H2 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 H2 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. |
| Databáze: | OpenAIRE |
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