Temperature- and Pressure-Dependent Kinetics of CH ₂ OO + Methacrolein and CH ₂ OO + Methyl Vinyl Ketone Reactions: A Theoretical Study

Methacrolein (MACR) and methyl vinyl ketone (MVK) are the coproducts of Criegee intermediates (CIs) from isoprene ozonolysis, and the reaction between them has potential importance in the atmospheric degradation of volatile organic compounds. This work investigates the reaction mechanism and kinetics of the smallest Criegee intermediate, CH₂OO, with MACR and MVK. 1,3-Cycloaddition of CH₂OO across the C═O double bond forms a secondary ozonide (SOZ), which may decompose to organic acids and carbonyl compounds. The lowest-energy-dissociation pathway for the SOZ involves the formation of a singlet biradical intermediate (BIR) by ring fission, followed by H-shift isomerization and dissociation to products. Master equation (ME) calculations show that the rate constants show a negative temperature effect in the temperature range of 200-500 K for the reaction of CH₂OO with MACR and MVK. The collisionally stabilized SOZ was found to be the main products at 300 K and atmospheric pressure, which tend to decompose to organic acids and carbonyl compounds at high temperatures and low pressures.