LIF studies of iodine oxide chemistry Part 3. Reactions IO + NO3 → OIO + NO2, I + NO3 → IO + NO2, and CH2I + O2 → (products): implications for the chemistry of the marine atmosphere at night

Abstract

The technique of pulsed laser photolysis coupled to LIF detection of IO was used to study reactions: (R1a) IO + NO₃ → OIO + NO₂; (R2) I + NO₃ → (products); (R3) CH₂I + O₂ → (products); and (R4) O(³P) + CH₂I₂ → IO + CH₂I, at ambient temperature. Reaction (R1) was observed for the first time in the laboratory and a rate coefficient of k_{1 a} = (9 ± 4) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ obtained. For (R2), a value of k₂ (298 K) = (1.0 ± 0.3) × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹ was obtained, and a IO product yield close to unity determined. IO was also formed in a close-to-unity yield in reaction (R4), whereas in (R3) an upper limit of α₃(IO) < 0.12 was derived. The implications of these results for the nighttime chemistry of the atmosphere were discussed. Box model calculations showed that efficient OIO formation in (R1a) was necessary to explain field observations of large OIO/IO ratios.