Laser flash photolysis of Cl 2 /CH 3 OH/O 2 /I 2 /NO 2 /SF 6 /N 2 mixtures at 308 nm has been coupled with simultaneous time-resolved detection of HO 2 (by infrared tunable diode laser absorption spectroscopy) and IO (by visible absorption spectroscopy) to investigate the kinetics of the atmospherically important reaction HO 2 + IO → products over the temperature range 274−373 K in N 2 buffer gas at pressures of 12 and 25 Torr. All experiments were performed under near pseudo-first-order conditions with HO 2 in excess over IO. At 298 K, the rate coefficient was determined to be (9.7 ± 2.9) × 10 -11 cm 3 molecule -1 s -1, with the primary source of uncertainty being knowledge of the infrared line strength(s) required to convert measured HO 2 absorbances to absolute concentrations. The temperature dependence of the HO 2 + IO rate coefficient was found to be adequately described by the Arrhenius expression k = 9.3 × 10 -12 exp(680/ T ) cm 3 molecule -1 s -1 . The results reported in this study are compared with other recent studies of HO 2 + IO kinetics, and the potential roles of this reaction in atmospheric chemistry are discussed.
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Cronkhite et al. (1999) studied this question.