Kinetics of the Gas-Phase Reactions of syn- and anti-CH(3)CHOO Criegee Intermediate Conformers with SO(2) as a Function of Temperature and Pressure.

Kinetics of reactions between SO(2) and CH(3)CHOO Criegee intermediate conformers have been measured at temperatures between 242 and 353 K and pressures between 10 and 600 Torr using laser flash photolysis of CH(3)CHI(2)/O(2)/N(2)/SO(2) gas mixtures coupled with time-resolved broadband UV absorption spectroscopy. The kinetics of syn-CH(3)CHOO + SO(2) are pressure-dependent and exhibit a negative temperature dependence, with the observed pressure dependence reconciling apparent discrepancies between previous measurements performed at ∼298 K. Results indicate a rate coefficient of (4.80 ± 0.46) × 10(-11) cm(3) s(-1) for the reaction of syn-CH(3)CHOO with SO(2) at 298 K and 760 Torr. In contrast to the behavior of the syn-conformer, the kinetics of anti-CH(3)CHOO + SO(2) display no significant dependence on temperature or pressure over the ranges investigated, with a mean rate coefficient of (1.18 ± 0.21) × 10(-10) cm(3) s(-1) over all conditions studied in this work. Results indicate that the reaction of syn-CH(3)CHOO with SO(2) competes with unimolecular decomposition and reaction with water vapor in areas with high SO(2) concentration and low humidity, particularly at lower temperatures.