Chemical Models Of Adenine Precursors Cyanamide And Carbodiimide In The Interstellar Medium

By Keith Cowing
Status Report
March 7, 2023
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Chemical Models Of Adenine Precursors Cyanamide And Carbodiimide In The Interstellar Medium
The calculated abundances of NH2CN and HNCNH in the gas phase and on grain mantles, including surface and icy mantle for our C-type shock models. The results are plotted versus time after cold core models with the evolution time of 3, 5×105 yr at pre-shock temperatures of 20 K with higher 𝜁 . Solid lines correspond to the gas-phase abundances, and dotted lines indicate abundances on the grains. The gray rectangle represents the observed abundance with ± a factor of 3 uncertainty for NH2CN in G+0.693. Golden dotted lines denote temperature profiles. — astro-ph.GA

Cyanamide (NH2CN) and its isomer, carbodiimide (HNCNH), may form adenine in the interstellar medium (ISM) via a series of reactions.

Therefore, they are considered key prebiotic molecules in the study of the origin of life. We used the three-phase NAUTILUS chemical code, which includes the gas, the dust surface, and the icy mantle, to investigate the formation and destruction of cyanamide and carbodiimide. We added over 200 new chemical reactions of the two isomers and related species, and established a relatively complete network.

We applied cold core, hot corino/core and shock models to simulate the different physical environments, and found that the two isomers are mainly produced by the free radical reactions on grain surfaces. Our simulated results suggest that cyanamide and carbodiimide molecules come from surface chemistry at early evolutionary stages. Then they are released back to the gas phase, either by thermal process (in hot cores, hot corinos) or shock-induced desorption (in shock regions).

We speculate that it is an inefficient route to form a tautomer of adenine by starting from molecules cyanoacetylene (C3NH), cyanamide and carbodiimide in ISM.

Xia Zhang, Donghui Quan, Runxia Li, Jarken Esimbek, Long-Fei Chen, Guoming Zhao, Yan Zhou

Comments: 13 pages, 6 figures, 7 tables, accepted for publication in MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2303.01854 [astro-ph.GA] (or arXiv:2303.01854v1 [astro-ph.GA] for this version)
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Submission history
From: Xia Zhang
[v1] Fri, 3 Mar 2023 11:16:17 UTC (305 KB)
Astrobiology, Astrochemistry

SpaceRef co-founder, Explorers Club Fellow, ex-NASA, Away Teams, Journalist, Space & Astrobiology, Lapsed climber.