Open AccessThe effect of grain size distribution on H 2 formation rate in the interstellar medium
Author(s) -
Lipshtat Azi,
Biham Ofer
Publication year - 2005
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.1365-2966.2005.09356.x
Subject(s) - physics , interstellar medium , grain size , hydrogen , molecular cloud , cosmic dust , interstellar cloud , astrochemistry , chemical physics , astrophysics , volume (thermodynamics) , star formation , particle size distribution , thermodynamics , galaxy , chemistry , materials science , particle size , stars , composite material , quantum mechanics
The formation of molecular hydrogen (H 2 ) in the interstellar medium takes place on the surfaces of dust grains. Hydrogen molecules play a role in gas‐phase reactions that produce other molecules, some of which serve as coolants during gravitational collapse and star formation. Thus, the evaluation of the production rate of hydrogen molecules and its dependence on the physical conditions in the cloud are of great importance. Interstellar dust grains exhibit a broad size distribution in which the small grains capture most of the surface area. Recent studies have shown that the production efficiency strongly depends on the grain composition and temperature as well as on its size. In this paper, we present a formula that provides the total production rate of H 2 per unit volume in the cloud, taking into account the grain composition and temperature as well as the grain size distribution. The formula agrees very well with the master equation results. It shows that for a physically relevant range of grain temperatures, the production rate of H 2 is significantly enhanced due to their broad size distribution.