Kinetics of C2 (a3Πu) reactions with sulfur containing molecules

Rate constants for the reactions of C2 (a3Πu) with H2S, SO2 and CS2 were measured under pseudo-first-order conditions at 298 K and 6.5 Torr total pressure. C2 (a3Πu) radicals were generated by photolysis of C2Cl4 with the focused output from the fourth harmonic of a Nd:YAG laser at 266 nm. The relative concentration of C2 (a3Πu) radicals was monitored in the (0, 0) band of the C2 (d3Πg←a3Πu) transition at 516.5 nm by laser-induced fluorescence (LIF). The rate constants obtained (cm3 molecule−1 s−1) are kH2S=(8.90±0.51)×10−12, kSO2=(2.33±0.17)×10−12 and kCS2=(1.59±0.08)×10−10, respectively. The errors given are 1σ. The obtained rate constant for the reaction of C2 (a3Πu) with CS2 is quite large and near the theoretical gas kinetic collision frequency. Ab initio calculations were performed in order to gain an insight into the mechanism. Theoretical calculation shows that the primary step of the reaction proceeds via addition without a barrier, which is consistent with experimental results.