Investigating The Impact of Reactions Of C And CH With Molecular Hydrogen On A Glycine Gas-grain Network

By Keith Cowing
Status Report
January 11, 2023
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Investigating The Impact of Reactions Of C And CH With Molecular Hydrogen On A Glycine Gas-grain Network
Time series of the abundances of grain-surface and gas-phase NH2CH2 and NH2CH3 in Phase 1 of a dark cloud. Furthermore, we observe that the inclusion of the dihydrogenation reactions, regardless of efficiency 𝛼 severely depletes the abundances of the glycine precursors in both phases relative to the original model which did not include either of the dihydrogenation reactions. Also plotted are the limits of detectability we have used for gas and grain-surface species. We do not plot glycine, as it is not formed at all in Phase 1. We observe that only the original model is capable of producing ’detectable’ levels of methylamine and the methylamine radical. For the other configurations, an increase in 𝛼 results in increased depletion of the species relative to the original model. We also observe that enhanced cosmic ray ionisation depletes the abundances on the grains but not in the gas. — physics.chem-ph

The impact of including the reactions of C and CH with molecular hydrogen in a gas-grain network is assessed via a sensitivity analysis.

To this end, we vary 3 parameters, namely, the efficiency for the reaction C + H2 -> CH2, and the cosmic ray ionisation rate, with the third parameter being the final density of the collapsing dark cloud. A grid of 12 models is run to investigate the effect of all parameters on the final molecular abundances of the chemical network.

We find that including reactions with molecular hydrogen alters the hydrogen economy of the network; since some species are hydrogenated by molecular hydrogen, atomic hydrogen is freed up. The abundances of simple molecules produced from hydrogenation, such as CH4, CH3OH and NH3, increase, and at the same time, more complex species such as glycine and its precursors see a significant decrease in their final abundances.

We find that the precursors of glycine are being preferentially hydrogenated, and therefore glycine itself is produced less efficiently.

Johannes Heyl, Thanja Lamberts, Serena Viti, Jonathan Holdship

Comments: 11 pages, 3 figures, accepted for publication in MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA); Chemical Physics (physics.chem-ph)
Cite as: arXiv:2301.04324 [astro-ph.GA] (or arXiv:2301.04324v1 [astro-ph.GA] for this version)
Submission history
From: Johannes Heyl
[v1] Wed, 11 Jan 2023 06:21:52 UTC (760 KB)
Astrochemistry, Astrobiology

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