Hydrogenation of Small Aromatic Heterocycles at Low Temperatures
MNRAS 000,1–8 (2021) Preprint 25 May 2021 Compiled using MNRAS LATEX style file v3.0 Hydrogenation of small aromatic heterocycles at low temperatures April M. Miksch,1 Annalena Riffelt,1 Ricardo Oliveira,2 Johannes Kästner,1 and Germán Molpeceres,1¢ 1Institute for Theoretical Chemistry, University of Stuttgart, Stuttgart, Germany 2Chemistry Institute, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil Accepted XXX. Received YYY; in original form ZZZ ABSTRACT The recent wave of detections of interstellar aromatic molecules has sparked interest in the chemical behavior of aromatic molecules under astrophysical conditions. In most cases, these detections have been made through chemically related molecules, called proxies, that implicitly indicate the presence of a parent molecule. In this study, we present the results of the theoretical evaluation of the hydrogenation reactions of different aromatic molecules (benzene, pyridine, pyrrole, furan, thiophene, silaben- zene, and phosphorine). The viability of these reactions allows us to evaluate the resilience of these molecules to the most important reducing agent in the interstellar medium, the hydrogen atom (H). All significant reactions are exothermic and most of them present activation barriers, which are, in several cases, overcome by quantum tunneling. Instanton reaction rate constants are provided between 50 K and 500 K. For the most efficiently formed radicals, a second hydrogenation step has been studied. We propose that hydrogenated derivatives of furan, pyrrole, and specially 2,3-dihydropyrrole, 2,5-dihydropyrrole, 2,3-dihydrofuran, and 2,5-dihydrofuran are promising candidates for future interstellar detections. Key words: ISM: molecules – Molecular Data – Astrochemistry – methods: numerical 1 INTRODUCTION (Campbell et al.
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