paper

Effect of surface H $_{2}$ on molecular hydrogen formation on interstellar grains

arXiv:2203.03877 · doi:10.1093/mnras/stac655

Abstract

We investigate how the existence of hydrogen molecules on grain surfaces may affect H $_{2}$ formation efficiency in diffuse and translucent clouds. Hydrogen molecules are able to reduce the desorption energy of H atoms on grain surfaces in models. The detailed microscopic Monte Carlo method is used to perform model simulations. We found that the impact of the existence of H $_{2}$ on H $_{2}$ formation efficiency strongly depends on the diffusion barriers of H $_{2}$ on grain surfaces. Diffuse cloud models that do not consider surface H $_{2}$ predict that H atom recombination efficiency is above 0.5 over a grain temperature (T) range 10 K and 14 K. The adopted H $_{2}$ diffusion barriers in diffuse cloud models that consider surface H $_{2}$ are 80 $%$ H $_{2}$ desorption energies so that H $_{2}$ can be trapped in stronger binding sites. Depending on model parameters, these diffuse cloud models predict that the recombination efficiency is between nearly 0 and 0.5 at 10 K $\leq$ T $\leq$ 14 K. Translucent cloud model results show that H $_{2}$ formation efficiency is not affected by the existence of surface H $_{2}$ if the adopted average H $_{2}$ diffusion barrier on grain surfaces is low (194 K) so that H $_{2}$ can diffuse rapidly on grain surfaces. However, the recombination efficiency can drop to below 0.002 at T $\geq$ 10 K if higher average H $_{2}$ diffusion barrier is used (255 K) in translucent cloud models.

accepted for publication in MNRAS

Effect of surface H2​ on molecular hydrogen formation on interstellar grains

Abstract

Effect of surface H $_{2}$ on molecular hydrogen formation on interstellar grains