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

The laser-flash photolysis technique combined with resonance fluorescence d etection of OH was used to investigate the kinetics of the title reaction a t temperatures between 246 and 353 K and at a total pressure of 75 +/- 1 To rr Ar. Under these conditions the rate coefficient shows a negative tempera ture dependence which is described by k(4)(246-353 K) = 7.0(-0.4)(+1.9) x 1 0(-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 re action mechanism that proceeds without a significant activation barrier. Th e room temperature (294 K) rate constant is k(4) = 6.5(-0.4)(+2) x 10(-11) cm(3) s(-1), which is significantly larger than previous measurements. Reas ons for this difference and the implications of the new rate coefficients f or the lifetime of HI in the atmosphere are discussed.