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

Abstract We use microscopic Monte Carlo simulation techniques to investigate the impact of H 2 diffusion energy on the recombination efficiency of H 2 on interstellar dust grain surfaces under diffuse and translucent cloud conditions. We constructed five models representing different possible conditions encountered by adsorbed H and H 2 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 H 2 on dust surfaces decreases as H 2 diffusion energy increases. An interesting finding of this work is that considering different binding sites for H and H 2 gives rise to multiple steady phases, during which the recombination efficiency remains constant with a change in H 2 diffusion energy.