$H_2$ formation on interstellar grains in different physical regimes
O. Biham, I. Furman, N. Katz, V. Pirronello, G. Vidali;
MNRAS, 1998, 296, 869

ABSTRACT:An analysis of the kinetics of H_2 formation on interstellar dust grains is presented using rate equations. It is shown that semi-empirical expressions that have appeared in the literature represent two different physical regimes. In particular, it is shown that the expression given by Hollenbach, Werner & Salpeter applies when high flux, or high mobility, of H atoms on the surface of a grain makes it very unlikely that H atoms evaporate before they meet each other and recombine. The expression of Pirronello et al. - deduced on the basis of accurate measurements of a realistic dust analogue - applies to the opposite regime (low coverage and low mobility). The implications of this analysis for the understanding of the processes dominating in the interstellar medium are discussed.
KEYWORDS: atomic processes, molecular processes, ism: abundances, ism: atoms, ism: molecules
PERSOKEY:h2, general ism, dust, ,
CODE: biham98