Abstract
The discharge-flow resonance fluorescence technique has been used to determine the absolute rate constant for the reaction OH + HO/sub 2/ ..-->.. H/sub 2/O + O/sub 2/ from 254 to 382 K at a total pressure of 1 Torr. Pseudo-first-order conditions were used with HO/sub 2/ in large excess over OH. The rate constant was obtained directly from observed decays of OH and measured concentrations of HO/sub 2/. Since the observed rate constant was found to be very sensitive to small background concentrations of O and H atoms, NO/sub 2/ was used to remove both atoms species from the system. With added NO/sub 2/ the result at 299 K is (1.1 +/- 0.3) x 10/sup -10/ cm/sup 3/ molecule/sup -1/ s/sup -1/ where the error limits are one standard deviation and include an estimate of overall experimental uncertainty. The temperature dependence expressed in Arrhenius form is (4.8 +/- 0.8) x 10/sup -11/ exp((250 +/- 50)/T). The results are independent of the type of reactor surface and the precursor used to produce OH and HO/sub 2/. The present results agree well with earlier measurements near 1-atm total pressure and suggest that this rate constant exhibits little or no pressure dependence betweenmore » 1 and 1000 Torr.« less
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