Reaction of carbon atoms, C (2p(2),P-3), with hydrogen sulfide, H2S (X(1)A(1)): Overall rate constant and product channels

The multichannel C + H2S reaction was studied, at room temperature, in a lo w-pressure fast-flow reactor. Carbon atoms were obtained from the reaction of CBr4 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 lim it. Absolute product branching ratio was estimated over the channels yieldi ng H atoms probed by resonance fluorescence in the vacuum ultraviolet: H HCS or HSC (75 +/- 25)%. Ab initio studies of the different stationary poin ts relevant to this reaction have been performed at the CCSD(T)/cc-pVTZHQCI SD/cc-pVDZ level. In agreement with the measured rate constant, the inserti on transition structure leading to triplet HSCH is found lower in energy th an the reactants. The reaction is found to proceed via H2SC ((3)A'') interm ediate that then rearrange to HSCH. On the basis of RRKM calculations, this last species leads mainly to HCS + H products.