Temperature-Dependent Kinetics of the Reactions of the Criegee Intermediate CH₂OO with Aliphatic Aldehydes

Criegee intermediates, formed by alkene ozonolysis in the troposphere, can react with volatile organic compounds (VOCs). The temperature-dependent kinetics of the reactions between the Criegee intermediate CH₂OO and three aliphatic aldehydes, RCHO where R = H, CH₃, and C₂H₅ (formaldehyde, acetaldehyde, and propionaldehyde, respectively), have been studied using a laser flash-photolysis transient absorption spectroscopy technique. The experimental measurements are supported by <i>ab initio</i> calculations at various composite levels of theory that characterize stationary points on the reaction potential and free energy surfaces. As with other reactions of CH₂OO with organic carbonyls, the mechanisms involve 1,3-dipolar cycloaddition at the C=O group, over submerged barriers, leading to the formation of 1,2,4-trioxolane secondary ozonides. The bimolecular rate constants of all three reactions decrease with increasing temperature over the range 275-335 K and are characterized by equations of Arrhenius form: <i>k</i>(<i>T</i>) = (7.1 ± 1.5) × 10^-14exp((1160 ± 60)/<i>T</i>), (8.9 ± 1.7) × 10^-15exp((1530 ± 60)/<i>T</i>), and (5.3 ± 1.3) × 10^-14exp((1210 ± 70)/<i>T</i>) cm³ s^-1 for HCHO, CH₃CHO, and C₂H₅CHO, respectively. Based on estimated concentrations of CH₂OO, the reactions with aldehydes are unlikely to play a significant role in the atmosphere.