Open AccessAre molecule‐covered dust grains efficient catalysts of H 2 formation in the cold ISM?
Author(s) -
Gavilan L.,
Lemaire J. L.,
Vidali G.
Publication year - 2012
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2012.21463.x
Subject(s) - desorption , thermal desorption , chemical physics , molecule , hydrogen , astrochemistry , exothermic reaction , deuterium , interstellar medium , diffusion , thermal desorption spectroscopy , chemistry , catalysis , adsorption , materials science , atomic physics , physics , astrophysics , thermodynamics , organic chemistry , galaxy
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 < 10 K and T gas ∼ 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 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.