Kinetics and mechanism of hydroxyl reactions with organic sulfides

Abstract

The conventional flash photolysis-resonance fluorescence technique was employed to study reactions of OH with CH/sub 3/SCH/sub 3/ (1), CD/sub 3/SCD/sub 3/ (2), CH/sub 3/SC/sub 2/H/sub 5/ (3), and C/sub 2/H/sub 5/SC/sub 2/H/sub 5/ (4) in argon buffer gas. Reactivity trends, temperature dependencies, and isotope effects suggest that hydrogen abstraction is the dominant observed reaction pathway under these conditions. A pulsed-laser photolysis-pulsed-laser-induced fluorescence technique was employed to study reactions 1 and 2 in N/sub 2/, air, and O/sub 2/ buffer gases. Complex kinetics were observed in the presence of O/sub 2/. A four-step mechanism involving hydrogen abstraction, reversible addition to the sulfur atom, and scavenging of the (thermalized) adduct by O/sub 2/ is required to explain all experimental observations. In 1 atm of air, the effective bimolecular rate constant for reaction 1 decreases monotonically from 1.58 x 10/sup -11/ to 5.2 x 10/sup -12/ cm/sup 3/ molecule/sup -1/s/sup -1/ over the lower tropospheric temperature range 250-310 K. Over the same temperature range the branching ratio for hydrogen abstraction increases monotonically from 0.24 to 0.87. At 261 K, the rate constant for unimolecular decomposition of the CD/sub 3/S(OH)CD/sub 3/ adduct is (3.5 +/- 2.0) x 10/sup 6/ s/sup -1/ and the rate more » constant for the adduct reaction with O/sub 2/ is (4.2 +/- 2.2) x 10/sup -12/ cm/sup 3/ molecule/sup -1/s/sup -1/. « less