2008ApJ...681.1717K

The dissociative recombination (DR) of D₃S⁺ has been studied at the heavy ion storage ring CRYRING. The absolute DR cross sections have been measured over the interaction energy range between ∼0 and 0.1 eV, and the energy-dependent cross section obtained is best fitted by the expression σ(E)=(1.3±0.3)x10^–16E^{–1.36±0.04} cm2. From the cross section the thermal rate coefficient has been deduced to be (2.8±0.7)x10^–7(T/300)^{–0.86±0.03}cm3/s^. The branching fractions in the reaction have been measured at ∼0 eV collision energy. The break-up into D₂S+D occurs with a probability of only 0.17±0.08, whereas the three-body channel DS+2D dominates with a probability of 0.58±0.11. The remaining channels DS+D₂ and S+D₂+D contribute with 0.15±0.07 and 0.10±0.06, respectively. The impact of these results on the sulfur chemistry and deuterium fractionation in dark molecular clouds was investigated through chemical kinetic models. With these data, the calculated fractional abundance of H₂ S is lower than observed in TMC-1, which supports the assertion that H₂ S is formed on grain surfaces and not through gas-phase reactions.