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The kinetics of the recombination reaction, OH+NO 2 +(M)fHNO 3 +(M) have been investigated by the pulsed laser photolysis-pulsed laser induced fluorescence (PLP-PLIF) technique in air, nitrogen, oxygen, and helium buffer gases at room temperature and as a function of pressure (30-700 Torr). Additional measurements in nitrogen at 273 K (100-700 Torr) are reported. The third-body efficiency of water vapor has also been investigated. Our values for the absolute rate coefficient in nitrogen at room temperature and at 273 K are in excellent agreement with the JPL 1994 recommendation but lie substantially above the current JPL 2000 recommendation. Our rate coefficients in helium agree with previous literature studies, suggesting that systematic errors are small. Oxygen is found to be about 20% less efficient than nitrogen, and we see no significant enhancement in recombination in the presence of water vapor. Our results suggest that formation of the pernitrous acid isomer cannot explain the discrepancies in the current experimental database.

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The kinetics and mechanism of the three-body recombination of OH with NO2 were studied using a pulsed laser photolysis pulsed laser induced fluorescence technique. The rate coefficients for deactivation of vibrationally excited OH (v = 1-5) by NO2 were found to be independent of vibrational level with a value of (6.4 +/- 0.3) x 10(-11) cm3 molecule s (-1) at 298 K. The rate coefficient for reaction of 18OH with NO2 was measured and found to be much faster than for unlabeled OH with a "zero pressure" rate of 1 x 10(-11) cm3 molecule(-1) s(-1) at 298 K and 273 K. Observation of temporal profiles of 16OH and 18OH suggest that isotopic scrambling in the initially formed [H18ON16O2] complex is complete on the microsecond time scale of our experiments. The rate coefficient for reaction of unlabeled OH with NO2 was measured at 413 K in 400 Torr of He. Biexponential temporal profiles were obtained and are consistent with a 10 +/- 3% yield of the weakly bound HOONO isomer.

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