Molecular Hydrogen Formation During Dense Interstellar Cloud Collapse

Abstract

We study the evolution of molecular hydrogen on the grain surfaces and in the gas phase using both the rate equation (which tracks the average number of molecules) and the master equation (which tracks the expectation values of molecules). We show that above a certain critical accretion rate of $H$ on the grains, the results from these two methods become identical. We used this result to follow the collapse of a dense interstellar cloud and studied the formation of molecular hydrogen for two different temperatures (T=10K and 12K) and two different masses ($1M_{\odot }$ and $10M_{\odot }$) of the cloud when olivine grains were used. Since at higher temperatures, the recombination is very small for these grains, we also studied a similar hydrodynamic processes at higher temperatures (T=20K and 25K) when amorphous carbon grains were used. We find that generally, for olivine grains, more than 90% $H$ is converted to $H_2$ within $\sim 10^{5-7}$yr whereas for amorphous grains it takes $\sim 10^{6-7}$yr. $H_2$ formed in this manner can be adequate to produce the observed complex molecules.

19 pages, 10 figures, MNRAS (submitted)

References in corpus (8)

• Molecular hydrogen formation in the interstellar medium
• Molecular Cloud Formation Behind Shock Waves
• Master Equation for Hydrogen Recombination on Grain Surfaces
• The dust temperature distribution in prestellar cores
• The structure and stability of molecular cloud cores in external radiation fields
• On the master equation approach to diffusive grain-surface chemistry: the H, O, CO system
• Enhanced production of HD and D_2 molecules on small dust grains in diffuse clouds
• Diffusive grain-surface chemistry involving the atoms and diatomic molecules of two elements

Cited by in corpus (4)

• Formation of water and methanol in star forming molecular clouds
• Effects of Initial Condition and Cloud Density on the Composition of the Grain Mantle
• Effective grain surface area in the formation of molecular hydrogen in interstellar clouds
• Time evolution of simple molecules during proto-star collapse