Can interstellar H2S be formed via gas-phase reactions? Calculations concerning the rates of the ternary and radiative association reactions between HS+ and H2

Based on laboratory work involving the ternary association reaction of HS+ and H2 at 80 K, we have estimated the rate of the analogous radiative association reaction under interstellar conditions. Both the ternary and radiative association reactions appear to occur via a mechanism in which the electronic spin of the H3S+ complex changes before the complex is stabilized. Although this spin change is of low probability, it leads to a radiative association rate coefficient at 80 K of $7\times10^{-16}\enspace \text {cm}^3 \enspace \text s^{-1}$ if radiative stabilization occurs at a rate of 103 s−1. This value of the radiative association rate coefficient at 80 K is large enough to lead to the observed abundance of H2S in the ambient ridge source in Orion.