Kinetics of the Reaction of OH with HI between 246 and 353 K

The laser-flash photolysis technique combined with resonance fluorescence detection of OH was used to investigate the kinetics of the title reaction at temperatures between 246 and 353 K and at a total pressure of 75 ± 1 Torr Ar. Under these conditions the rate coefficient shows a negative temperature dependence which is described by k 4 (246−353 K) = × 10 -11 ( T /298) -1.5±0.5 cm 3 s -1 . Both the large rate coefficient and trends in the reactivity of OH with HCl, HBr, and HI are suggestive of a reaction mechanism that proceeds without a significant activation barrier. The room temperature (294 K) rate constant is k 4 = × 10 -11 cm 3 s -1, which is significantly larger than previous measurements. Reasons for this difference and the implications of the new rate coefficients for the lifetime of HI in the atmosphere are discussed.