Gas-Phase Reactions of H2CS and H2CO with CN: Similarities and Differences from a Computational Study

The gas-phase reaction of H2CS with the CN radical has been investigated with the aim of understanding its evolution in the interstellar medium (ISM). After the detection of thioformyl cyanide in TMC-1, this process has been incorporated into astrochemical models because it is considered the most efficient (if not the only) gas-phase formation route for such a molecule in dark molecular clouds. However, neither experimental nor theoretical studies have been reported in the literature regarding its feasibility in the typical conditions of the ISM. In this work, the corresponding reactive potential energy surface has been accurately investigated and complemented by ab initio transition state theory calculations to derive global rate coefficients. In view of the potential similarities between the H2CS + CN and H2CO + CN reactions, this latter process has also been reinvestigated. The availability of experimental data for the H2CO + CN reaction has been exploited to derive the accuracy of the computed rate constants for the sulfur-bearing counterpart.