Gas-phase formation route for trans-HC(O)SH and its isomers under interstellar conditions: a state-of-the-art quantum-chemical study

Sulphur is an important and ubiquitous element of the interstellar medium (ISM). Despite its importance, its chemistry still needs to be elucidated, with one of the main issues being the missing sulphur problem. In this work, small molecular species, already detected in the ISM (SH, OH, H2CS, H2CO, H2S, H2O, HCS/HSC, and HCO), were combined to set five different gas-phase reactions for the formation of isomers belonging to the CH2SO family, with one of its member, namely trans-HC(O)SH, already identified as well. Through a state-of-the-art computational study, it has been found that, thermochemically, only one of the reactions considered is open in the ISM conditions: H2CS + OH can produce cis/trans-HC(S)OH and cis/trans-HC(O)SH via hydrogen-atom loss. Kinetically, the favoured product is trans-HC(S)OH followed by trans-HC(O)SH. In view of the recent detection of this latter, our study suggests that trans-HC(S)OH is a good candidate for astronomical observations. Since this species has never been studied experimentally, as a first step towards its laboratory characterization, accurate estimates of the rotational constants have been provided.