Experimental and theoretical investigations of rate coefficients of the reaction S(P-3)+O-2 in the temperature range 298-878 K

Abstract

Rate coefficients of the reaction S+O-2 with Ar under 50 Torr in the temperature range 298-878 K were determined with the laser photolysis technique. S atoms were generated by photolysis of OCS with a KrF excimer laser at 248 nm; their concentration was monitored via resonance fluorescence excited by atomic emission of S produced from microwave-discharged SO2. Our measurements show that k(298 K)=(1.92+/-0.29)x10(-12) cm(3) molecule(-1) s(-1), in satisfactory agreement with previous reports. New data determined for 505-878 K show non-Arrhenius behavior; combining our results with data reported at high temperatures, we derive an expression k(T)=(9.02+/-0.27)x10(-19)T(2.11+/-0.15) exp[(730+/-120)/T] cm(3) molecule(-1) s(-1) for 298less than or equal toTless than or equal to3460 K. Theoretical calculations at the G2M (RCC2) level, using geometries optimized with the B3LYP/6-311+G(3df) method, yield energies of transition states and products relative to those of the reactants. Rate coefficients predicted with multichannel RRKM calculations agree satisfactorily with experimental observations; the reaction channel via SOO((1)A') dominates at T<500 K, whereas channels involving formation of SOO((3)A") followed by isomerization to SO2 before dissociation, and formation of SOO((1)A") followed by direct dissociation, become important at high temperatures, accounting for the observed rapid increase in rate coefficient. (C) 2004 American Institute of Physics.