2020/05/19 by Christopher N. Shingledecker, Germán Molpeceres, Víctor Rivilla +2 · 2 citations
Physics and Astronomy · #astro-ph.GA #physics.chem-ph
paper · pdf · doi:10.3847/1538-4357/ab94b5
The Astrophysical Journal, accepted: 17 pages, 9 figures, 7 tables
arxiv created 2020/05/19 · arxiv updated 2020/07/22
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.