Kinetics of Hydroxyl Radical Reactions with Isotopically Labeled Hydrogen

Abstract

The rate coefficients for the reactions of hydroxyl radical (OH) with H2 (k1), HD (k2), and D2 (k3) were measured between ∼230 and ∼420 K to be k1= 7.21 × 10-20T2.69 exp(−1150/T), k2 = 5.57 × 10-20T2.7 exp(−1258/T), and k3 = 5.7 × 10-20T2.73 exp(−1580/T) cm3 molecule-1 s-1 using pulsed photolysis to generate OH and laser-induced fluorescence to detect it. Using the same method, the rate coefficients for the reactions of OD with H2 and D2 were measured to be equal to k1 and k3, respectively. In reaction 2, the yield of H was measured to be 0.17 ± 0.03 and 0.26 ± 0.05 at 250 and 298 K, respectively, by detecting it using CW Lyman-α resonance fluorescence. k2 was found to be half the sum of k1 and k3 over the entire temperature range of this study. The quoted uncertainties are at the 95% confidence level and include estimated systematic errors. On the basis of these findings it is suggested that most, if not all, of the reaction in the range of temperatures studied here may be occurring via tunneling of H/D atoms through the barrier.