Letter to the Editor

From interstellar carbon monosulfide to methyl mercaptan: paths of least resistance

Institute for Theoretical Chemistry, University Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany
e-mail: a.l.m.lamberts@lic.leidenuniv.nl

Received: 14 February 2018
Accepted: 20 May 2018

Abstract

The 29 reactions linking carbon monosulfide (CS) to methyl mercaptan (CH₃SH) via ten intermediate radicals and molecules have been characterized with relevance to surface chemistry in cold interstellar ices. More intermediate species than previously considered are found likely to be present in these ices, such as trans- and cis-HCSH. Both activation and reaction energies have been calculated, along with low-temperature (T > 45 K) rate constants for the radical-neutral reactions. For barrierless radical-radical reactions on the other hand, branching ratios have been determined. The combination of these two sets of information provides, for the first time, quantitative information on the full H + CS reaction network. Early on in this network, that is, early on in the lifetime of an interstellar cloud, HCS is the main radical, while later on this becomes first CH₂SH and finally CH₃S.