Hydrogenation of small aromatic heterocycles at low temperatures
  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.
