Tropospheric oxidation of methyl hydrotrioxide (CH3OOOH) by hydroxyl radical

Abstract

We have employed high level theoretical methods to investigate the oxidation of methyl hydrotrioxide by hydroxyl radical, which is of interest in atmospheric chemistry research. The reaction can proceed by abstraction of either the terminal hydrogen atom of OOH group producing CH₃O, O₂ and H₂O, or one hydrogen atom of the CH₃ group forming H₂CO, HO₂ and H₂O. The rate constants for both reactions at 298 K are computed to be 4.7 × 10⁻¹¹ and 2.1 × 10⁻¹² cm³ molecule⁻¹ s⁻¹, respectively, that is, the abstraction of terminal hydrogen atom of the OOH group is about 22 times faster than that of a hydrogen atom of the CH₃ group. The rate constant for the overall CH₃OOOH + OH reaction is computed to be 4.9 × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. Our calculations predict branching ratios between 99.0 and 93.9% for the formation of methoxy radical plus molecular oxygen and water, and between 1.0 and 6.1% for the formation of formaldehyde plus hydroperoxyl radical and water, in the 225–325 K temperature range. The lifetime of CH₃OOOH in the troposphere is predicted to range from of 1.8 hours at 225 K, up to 3.9 hours at 275 K and decreasing to 0.2 hours at 310 K. CH₃OOO and CH₂OOOH radicals have been also investigated.