Kinetic and modeling studies of the reaction S + H2S

The reaction of S (3PJ) with H2S in Ar bath gas has been characterized by the laser photolysis–resonance fluorescence technique over 300–1040 K. The observed second-order rate constants are found to be pressure-dependent below 700 K. The reaction has been modeled accurately as a combination of direct abstraction on the triplet surfaceS(3PJ)+H2S→2SHtogether with multi-well reactions on the singlet surface via intersystem crossingS(3PJ)+H2S→H2SS∗→HSSH∗+M→HSSH+MS(3PJ)+H2S→H2SS∗→HSSH∗→2SHSince the intersystem crossing has a low energy barrier (3 kJ mol−1), the spin-forbidden channels dominate at low-temperature, with the overall rate and product distribution being dependent on pressure. Above 800 K, the abstraction channel on the triplet surface becomes important and is dominant above 1000 K.