2014ApJ...792...89G

HNCS and NCSH molecules, recently discovered in the interstellar medium, are likely formed via the dissociative recombination of H₂NCS⁺ or HNCSH⁺ isomeric ions. Interstellar synthesis of the latter is discussed on theoretical grounds. The analysis of relevant potential energy surfaces suggests a key role for chemical processes in which CSH⁺ or HCS⁺ cations (most likely formed in CS + H₃⁺ collisions) react with NH₂ or NH₃. The astrochemical kinetic database (kida.uva.2011), appended with 7 sulfur-bearing molecules and 48 corresponding reactions, has been applied to model the evolution of HNCS, NCSH, and their cationic precursors in a quiescent molecular cloud. Based on the model and on spectroscopic predictions, for an object like TMC-1, we expect the total intensity of H₂NCS⁺ microwave lines to be comparable to that observed for HSCN. Theoretically derived molecular parameters, of interest for radio spectroscopy, are given for the most stable cations sharing the H₂NCS⁺ stoichiometry.