Kinetics and mechanism of the OH + CIO₂reaction

The rate constant k 1 for the reaction of OH radicals with CIO 2 molecules was measured in a discharge flow system over the temperature range 293 ≤ T ≤ 473 K and at low pressures, 0.5 ≤ P ≤ 1.4 torr, using electron paramagnetic resonance or laser‐induced fluorescence to monitor the pseudo first‐order decay of OH concentrations. At 293 K, the value obtained for k 1 was (7.2 ± 0.5) × 10 −12 cm 3 molecule −1 s −1 . Within the temperature range of this study, a negative temperature dependence was observed: k 1 = (4.50 ± 0.75) × 10 −13 exp[(804 ± 114)/ T ] cm 3 molecule −1 s −1 . HOCl was detected by mass spectrometry as a product of the reaction and was titrated using OH + Cl 2 as a source in the calibration experiments. A simulation of the mechanism of the OH + ClO 2 reaction indicated that HOCl was mainly produced in the first reaction step. Both this result and the observed T dependence of k 1 suggest that this reaction proceeds via an intermediate adduct with a cyclic geometry.