Kinetics of C 2 (a [formula omitted]) reactions with sulfur containing molecules

Abstract

Rate constants for the reactions of C 2 (a 3 Π u ) with H 2S, SO 2 and CS 2 were measured under pseudo-first-order conditions at 298 K and 6.5 Torr total pressure. C 2 (a 3 Π u ) radicals were generated by photolysis of C 2Cl 4 with the focused output from the fourth harmonic of a Nd:YAG laser at 266 nm. The relative concentration of C 2 (a 3 Π u ) radicals was monitored in the (0, 0) band of the C 2 (d 3 Π g ← a 3 Π u ) transition at 516.5 nm by laser-induced fluorescence (LIF). The rate constants obtained (cm 3 molecule −1 s −1) are k H 2S =(8.90±0.51)×10 −12, k SO 2 =(2.33±0.17)×10 −12 and k CS 2 =(1.59±0.08)×10 −10, respectively. The errors given are 1 σ. The obtained rate constant for the reaction of C 2 (a 3Π u) with CS 2 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.