Reaction of carbon atoms, C (2p2,3P), with hydrogen sulfide, H2S (X1A1):: Overall rate constant and product channels

The multichannel C + H(2)S reaction was studied, at room temperature, in a low-pressure fast-flow reactor. Carbon atoms were obtained from the reaction of CBr(4) with potassium atoms. The overall rate constant was found to be (2.1 +/- 0.5) x 10(-10) cm(3) molecule(-1) s(-1), close to the gas kinetic limit. Absolute product branching ratio was estimated over the channels yielding H atoms probed by resonance fluorescence in the vacuum ultraviolet: H + HCS or HSC (75 +/- 25)%. Ab initio studies of the different stationary points relevant to this reaction have been performed at the CCSD(T)/cc-pVTZHQCISD/cc-pVDZ level. In agreement with the measured rate constant, the insertion transition structure leading to triplet HSCH is found lower in energy than the reactants. The reaction is found to proceed via H(2)SC ((3)A'') intermediate that then rearrange to HSCH. On the basis of RRKM calculations, this last species leads mainly to HCS + H products.