Isomers in Interstellar Environments (I): The Case of Z- and E-Cyanomethanimine

In this work, we present the results of our investigation into the chemistry of Z- and E-cyanomethanimine (HNCHCN), both of which are possible precursors to the nucleobase adenine.

Ab initio quantum chemical calculations for a number of reactions with atomic hydrogen were carried out. We find that the reaction H + Z/E-HNCHCN leading both to H-addition as well as H2-abstraction proceed via similar short-range barriers with bimolecular rate coefficients on the order of ∼10−17 cm3 s−1.

These results were then incorporated into astrochemical models and used in simulations of the giant molecular cloud G+0.693. The calculated abundances obtained from these models were compared with previous observational data and found to be in good agreement, with a predicted [Z/E] ratio of ∼3 – somewhat smaller than the previously derived value of 6.1±2.4. We find that the [Z/E] ratio in our simulations is due mostly to ion-molecule destruction rates driven by the different permanent dipoles of the two conformers. Based on these results, we propose a general rule-of-thumb for estimating the abundances of isomers in interstellar environments.

Christopher N. Shingledecker, Germán Molpeceres, Víctor Rivilla, Liton Majumdar, Johannes Kästner
Comments: The Astrophysical Journal, accepted: 17 pages, 9 figures, 7 tables
Subjects: Astrophysics of Galaxies (astro-ph.GA); Chemical Physics (physics.chem-ph)
Cite as: arXiv:2005.09477 [astro-ph.GA] (or arXiv:2005.09477v1 [astro-ph.GA] for this version)
Submission history
From: Christopher Shingledecker
[v1] Tue, 19 May 2020 14:23:52 UTC (5,404 KB)
https://arxiv.org/abs/2005.09477
Astrobiology, Astrochemistry