Molecular dynamics simulation of gaseous atomic hydrogen interactions with hydrocarbon grains

Semi-empirical molecular dynamics is used to simulate several gaseous atomic hydrogen interactions with hydrocarbon grains in space: recoil, adsorption, diffusion, chemisorption and recombination into molecular hydrogen. Their probabilities are determined by multiple numerical experiments, as a function of initial velocity of gas atoms. The equilibrium hydrogen coverage of free grains is then derived. These data can be used in calculations of material and energy balance as well as rates of hydrogen recombination on grains. The role of grain temperature is also considered.