Kinetics of Hydroxyl Radical Reactions with Isotopically Labeled Hydrogen

The rate coefficients for the reactions of hydroxyl radical (OH) with H 2 ( k 1 ), HD ( k 2 ), and D 2 ( k 3 ) were measured between ∼230 and ∼420 K to be k 1 = 7.21 × 10 -20 T 2.69 exp(−1150/ T ), k 2 = 5.57 × 10 -20 T 2.7 exp(−1258/ T ), and k 3 = 5.7 × 10 -20 T 2.73 exp(−1580/ T ) cm 3 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 H 2 and D 2 were measured to be equal to k 1 and k 3, 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. k 2 was found to be half the sum of k 1 and k 3 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.