Sticking coefficient of hydrogen and deuterium on silicates under interstellar conditions

Abstract

Sticking of H and D atoms on interstellar dust grains is the first step in molecular hydrogen formation, which is a key reaction in the InterStellar Medium (ISM). After studying the sticking coefficients of H2 and D2 molecules on amorphous silicate surfaces experimentally and theoretically, we extrapolate the results to the sticking coefficient of atoms and propose a formulae that gives the sticking coefficients of H and D on both silicates and icy dust grains. In our experiments, we used the King and Wells method for measuring the sticking coefficients of H2 and D2 molecules on a silicate surface held at 10 K. It consists of measuring with a QMS (quadrupole mass spectrometer) the signals of H2 and D2 molecules reflected by the surface during the exposure of the sample to the molecular beam at a temperature ranging from 20 K to 340 K. We tested the efficiency of a physical model, developed previously for sticking on water-ice surfaces. We applied this model to our experimental results for the sticking coefficients of H2 and D2 molecules on a silicate surface and estimated the sticking coefficient of atoms by a single measurement of atomic recombination and propose an extrapolation. Sticking of H, D, HD, H2, and D2 on silicates grains behaves the same as on icy dust grains. The sticking decreases with the gas temperature, and is dependent on the mass of the impactor. The sticking coefficient for both surfaces and impactors can be modeled by an analytical formulae S(T), which describes both the experiments and the thermal distribution expected in an astrophysical context. The parameters S0 and T0 are summarized in a table. Previous estimates for the sticking coefficient of H atoms are close to the new estimation; however, we find that, when isotopic effects are taken into account, the sticking coefficient variations can be as much as a factor of 2 at T=100 K.

7 pages and 3 Postscript figures. Published in Astronomy & Astrophysics journal AA-2011-17409

References in corpus (11)

• A model for atomic and molecular interstellar gas: The Meudon PDR code
• Water, O2 and Ice in Molecular Clouds
• Laboratory Synthesis of Molecular Hydrogen on Surfaces of Astrophysical Interest
• Desorption of CO and O2 interstellar ice analogs
• Mobility of D atoms on porous amorphous water ice surfaces under interstellar conditions
• Molecular Hydrogen Formation on Amorphous Silicates Under Interstellar Conditions
• Laboratory evidence for the non-detection of excited nascent H2 in dark clouds
• Gas temperature dependent sticking of hydrogen on cold amorphous water ice surfaces of interstellar interest
• Molecular Hydrogen Formation on Low Temperature Surfaces in Temperature Programmed Desorption Experiments
• H2 reformation in post-shock regions
• Molecular Hydrogen Formation on Porous Dust Grains

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