| Abstract
| - To reexamine the possibility of the spin-forbidden,molecular-elimination mechanism of the thermaldecomposition of H2S, H2S + M →S(3P) + H2 + M (1), recently indicated byexperimental and theoreticalstudies, as well as to examine the cause of discrepancies of its rateconstants among recent works, the reverseinsertion channel of the S(3P) + H2 reaction,S(3P) + H2 + M → H2S + M(−1), has been investigated. Theexperiments have been conducted with an excimer-laser photolysis (248nm) in a shock tube at a lowertemperature range, 900−1050 K, and a higher pressure range up to 4atm, than previous studies, where theinsertion process (−1) was estimated to be dominant over the simplehydrogen-atom-transfer reaction, S(3P)+ H2 → H + HS (2). The decay rate ofS(3P) atoms has been measured by using an atomicresonanceabsorption spectrometry technique. The measured rate constantagreed well with the extrapolation of theprevious measurements for reaction 2, showing that the recombinationchannel (−1) is still minor at theseexperimental conditions. The upper limit of the rate constant forreaction 1 derived in the present study wasshown to be consistent with the theoretical rate constant calculated bythe Troe's formula with the ab initiothreshold energy for the intersystem crossing and with reasonable weakcollision factors derived from therate constant for reaction 1 reported by Shiina et al. [J. Phys.Chem.1996, 100,2136].
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