KINETICS OF THE REACTION OF IODINE ATOMS WITH HO2 RADICALS

The rate coefficient (k7) for the reaction of iodine atoms with HO2 radicals, I + HO2 → HI + O2, has been measured directly with use of the discharge-flow/EPR technique, and the molecular-modulation/UV-absorption spectroscopy technique. Discharge-flow measurements were made under pseudo-first-order conditions with iodine atoms in large excess over HO2. Molecular-modulation measurements were made with iodine atoms in excess over HO2, but the I + HO2 reaction was occurring in competition with the self-reaction of HO2. The values of k7 determined at 298 K by these complementary methods agree within the combined experimental errors and provide a value of (3.8 ± 1.0) × 10-13 cm3 molecule-1 s-1. Further measurements made over the temperature range 283-353 K with the molecular-modulation technique allow recommendation of the following expression: k7 = (1.47 ± 0.63) × 10-11 exp(-(1090 ± 130)/T). The potential significance of this reaction as a sink for iodine in the troposphere and other aspects of tropospheric iodine chemistry are considered with a simple model of the atmospheric boundary layer. © 1990 American Chemical Society.