Understanding the Impact of H2 Diffusion Energy on the Formation Efficiency of H2 on the Interstellar Dust Grain Surface

We use microscopic Monte Carlo simulation techniques to investigate the impact of H2 diffusion energy on the recombination efficiency of H2 on interstellar dust grain surfaces under diffuse and translucent cloud conditions. We constructed five models representing different possible conditions encountered by adsorbed H and H2 on interstellar dust grains. We implemented adsorption sites with multiple binding energies for surface species; the Encounter-Desorption mechanism was also included. The study focused on silicate surfaces in diffuse clouds and water ice surfaces in translucent clouds. The results show that the recombination efficiency of H2 on dust surfaces decreases as H2 diffusion energy increases. An interesting finding of this work is that considering different binding sites for H and H2 gives rise to multiple steady phases, during which the recombination efficiency remains constant with a change in H2 diffusion energy.