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Sticking coefficient of hydrogen and deuterium on silicates under interstellar conditions | | H. Chaabouni
; H. Bergeron
; S. Baouche
; F. Dulieu
; E. Matar
; E. Congiu
; L. Gavilan
; J. L. Lemaire
; | | Date: |
11 Feb 2012 | | 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. | | Source: | arXiv, 1202.2473 | | Services: | Forum | Review | PDF | Favorites | |
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