Experimental and theoretical investigation of rate coefficients of the reaction S(3P)+OCS in the temperature range of 298-985 K

Chih Wei Lu, Yu Jong Wu, Yuan-Pern Lee*, R. S. Zhu, Ming-Chang Lin

*Corresponding author for this work

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22 Scopus citations

Abstract

The reaction S (P3) +OCS in Ar was investigated over the pressure range of 50-710 Torr and the temperature range of 298-985 K with the laser photolysis technique. S atoms were generated by photolysis of OCS with light at 248 nm from a KrF excimer laser; their concentration was monitored via resonance fluorescence excited by atomic emission of S produced from microwave-discharged S O2. At pressures less than 250 Torr, our measurements give k (298 K) = (2.7±0.5) × 10-15 cm3 molecule-1 s-1, in satisfactory agreement with a previous report by Klemm and Davis [J. Phys. Chem. 78, 1137 (1974)]. New data determined for 407-985 K connect rate coefficients reported previously for T860 and T≤478 K and show a non-Arrhenius behavior. Combining our results with data reported at high temperatures, we derived an expression k (T) = (6.1±0.3) × 10-18 T1.97±0.24 exp [- (1560±170) T] cm3 molecule-1 s-1 for 298≤TK≤1680. At 298 K and P500 Torr, the reaction rate was enhanced. Theoretical calculations at the G2M(CC2) level, using geometries optimized with the B3LYP6-311+G (3df) method, yield energies of transition states and products relative to those of the reactants. Rate coefficients predicted with multichannel Rice-Ramsperger-Kassel-Marcus (RRKM) calculations agree satisfactorily with experimental observations. According to our calculations, the singlet channel involving formation of SSCO followed by direct dissociation into S2 (a Δg1) +CO dominates below 2000 K; SSCO is formed via intersystem crossing from the triplet surface. At low temperature and under high pressure the stabilization of OCS2, formed via isomerization of SSCO, becomes important; its formation and further reaction with S atoms partially account for the observed increase in the rate coefficient under such conditions.

Original languageEnglish
Article number164329
JournalJournal of Chemical Physics
Volume125
Issue number16
DOIs
StatePublished - 1 Jan 2006

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