Recombination efficiency of molecular hydrogen on interstellar grains and its effect on pro duction of H/sub2/

Abstract

We study the efficiency of molecular hydrogen recombination on grain surfaces using both the rate equation (which tracks the average number of species) and the master equation (which tracks the expectation values of the species). We have incorporated Langmuir-Hinselwood rejection term in obtaining the efficiency. We use this result to compute H2 production rates as a function of the grain temperature and accretion rate of atomic hydrogen. Our general conclusion is that the H2 formation efficiency is very much dependent on the grain temperature and the accretion rate of the atomic hydrogen on grains. We provide tables of H2 production rates which could be readily used for future calculation of production of more complex molecules in the gas phase