Chemical Kinetic Study of the Reaction of CH₂OO with CH₃O₂

Criegee intermediates play an important role in the oxidizing capacity of the Earth's troposphere. Although extensive studies have been conducted on Criegee intermediates in the past decade, their kinetics with radical species remain underexplored. We investigated the kinetics of the simplest Criegee intermediate, CH₂OO, with the methyl peroxy radical, CH₃O₂, as a model system to explore the reactivities of Criegee intermediates with peroxy radicals. Using a multipass UV-Vis spectrometer coupled to a pulsed-laser photolysis flow reactor, CH₂OO and CH₃O₂ were generated simultaneously from the photolysis of CH₂I₂/CH₃I/O₂/N₂ mixtures with CH₂OO measured directly near 340 nm. We determined a reaction rate coefficient k_CH = (1.7 ± 0.5) × 10^-11 cm³ s^-1 at 294 K and 10 Torr, where the influence of iodine adducts is reduced. This rate coefficient is faster than previous theoretical predictions, highlighting the challenges in accurately describing the interaction between zwitterionic and biradical characteristics of Criegee intermediates.