| Abstract
| - The kinetics and products of reaction 1 between gas-phase BrO and IO radicals have been studied using thetechnique of laser photolysis with time-resolved UV−vis absorption spectroscopy. The O + IBr reaction 8,used as one source of IO and BrO radicals, was found to produce predominantly IO radicals at 295 K. Therate coefficient for reaction 8 is correlated with the branching ratio for IO production (channel 8a). Using avalue of 0.7 for the branching ratio for IO production (k8a/k8), k8 was found to be (3.6 ± 2.4) × 10-11 cm3molecule-1 s-1 at 295 K, with no significant temperature dependence between 210 and 333 K. Sensitivitytests using a kinetic model showed that, in addition to (1), decay traces were also sensitive to the rate coefficientfor reaction 12: I + BrO → Br + IO. This rate coefficient was found to be (1.3 ± 1.2) × 10-11 molecule-1cm3 s-1 at 295 K, with no significant temperature dependence between 235 and 333 K. The title reaction (1),IO + BrO → products was found to have a rate coefficient (8.5 ± 1.4) × 10-11cm3 molecule-1 s-1 at 295 K.Reaction 1 exhibited a negative temperature dependence between 210 and 333 K, adequately described by k1= (6.7 ± 0.8) × 10-12 exp ((760 ± 30)/T) molecules-1 cm3 s-1. No pressure dependence to k1 was foundbetween 100 and 760 Torr. All errors are 2σ. Five potential products exist for the IO + BrO reaction: IO +BrO → I + Br + O2 (1a), IO + BrO → IBr + O2 (1b), IO + BrO → OIO + Br (1c), IO + BrO → OBrO+ I (1d), and IO + BrO → IBrO2 (1e). No direct measurement of I or Br formation was perfomed. IBr wasobserved as a minor product (k1b/k1< 0.2). OIO formation was observed and shown to result from the IO +BrO reaction for the first time in this work. No evidence for OBrO formation was observed (k1d/k1< 0.15).No evidence for the formation or existence of IBrO2 was observed. The results obtained here, in conjunctionwith other published work, were used to constrain the branching ratio, α, for OIO production in the IO + IOreaction, giving {0.30 ± 0.05 ≤ α ≤ 0.46 ± 0.08}. This constraint allowed the absorption cross section ofOIO to be constrained giving (1.29 ± 0.22) ≥ σOIO × 1017 ≥ 0.87 ± 0.15) molecules-1 cm2 at the (5,1,0)peak at 549 nm, 295 K, and 760 Torr. Results are compared with previous studies of the IO + BrO reaction,and the atmospheric implications are briefly discussed.
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