A KINETIC-STUDY OF OH RADICAL REACTIONS WITH METHANE AND PERDEUTERATED METHANE

We measured absolute rate coefficients for the reactions of the hydrox yl radical with methane (k1) and methane-d4 (k2) using the laser photo lysis/laser-induced fluorescence technique. We characterized k1 and k2 over the temperature range 293-800 K at pressures between 400 and 750 Torr of helium. We find excellent agreement between our results and t he recent determinations of k1 at lower temperatures by Vaghjiani and Ravishankara. The measured rate coefficients, in the units cm3 Molecul e-1 s-1, fit well to the three-parameter expressions k1(T) = 9.65 x 10 (-20)T2.58 exp(-1082/T) and k2(T) = 8.70 X 10(-22)T3.23 exp(-1334/T). The kinetic isotope effect for abstraction of the H and D atoms varies from 6.75 at 293 K to 1.96 at 800 K. We compare our results to recent ly reported calculations by Melissas and Truhlar.