Hydrogenation of small aromatic heterocycles at low temperatures

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, silabenzene, 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.

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• Hydrogen abstraction reactions in formic and thioformic acid isomers by hydrogen and deuterium atoms. Insights on isomerism and deuteration
• Oxygen-bearing organic molecules in comet 67P's dusty coma: first evidence for abundant heterocycles
• Processing of hydroxylamine, NH2OH, an important prebiotic precursor, on interstellar ices
• Catalytic role of HI in the interstellar synthesis of complex organic molecule
• Hydrogenation of acetaldehyde on interstellar ice analogs reveals limited destruction
• Polyaromatic Hydrocarbons with an Imperfect Aromatic System as Catalysts of Interstellar H${}_2$ Formation