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ABSTRACT In the interstellar medium, chemical reactions proceed under conditions vastly different to those on Earth; these include extremely low temperatures and densities and take place in the gas phase and on water–ice grains. Understanding the energetics and more importantly the kinetics of such reactions is of relevance to the consequences on how terrestrial life emerged. Thermal reactions are largely absent if there is a substantial energy barrier but reactions proceeding by tunneling through the barrier can become important. Recent experiments conducted on an inert matrix at low temperatures showed that a 2‐seleno‐uracil, present in an oxo‐selenone conformation, irradiated with UV light was converted into a higher‐energy oxo‐selenol form which spontaneously reverted in the dark within hours. We show that hydrogen‐atom tunneling is solely responsible to explain this result and demonstrate that 2,4‐diseleno‐uracil would behave similarly but not 4‐seleno‐uracil within typical laboratory test times.
Würmel et al. (Fri,) studied this question.