Kinetics of the recombination reaction OH + H + M -> H2O + M at low temperatures.
A discharge flow resonance fluorescence technique (for the detection of OH) was used to det. the abs. rate of the reaction (1) OH + H + M -> H2O + M for M = He (in the range T = 230-300 K) and for M = Ar, N2, and CO2 (at 300 K). At total pressures of 3-11 torr reaction 1 is in its 3rd-order regime, where it can be sepd. from the 2nd-order (heterogeneous) recombination reaction (2) OH + H -> H2O. Specific rate consts. k1 at 300 K (in units of 10-31 cm6 molecule-2 s-1) are: 1.5, 2.3, 4.8, and 9 for M = He, Ar, N2 and CO2. The temp. variation of k1 for M = He can be represented by k1 = 4.3 * 10-25 T-2.6 cm6 molecule-2 s-1. The rate const. k2 was 2.7 * 10-14 cm3 molecules-1 s-1 and independent of temp. A comparison of k1 with results from high-temp. flame and shock tube expts. on both reaction 1 and the reverse dissocn. shows that low- and high-temp. data can be correlated in terms of a T-n dependence, with n being 2.0-2.2. Predictions of k1 by unimol. rate theory of the low-pressure-limiting rate consts. are in good agreement with the exptl. result.
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