Temperature-Dependent Kinetics of the Reactions of the Criegee Intermediate CHOO 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 CHOO and three aliphatic aldehydes, RCHO where R = H, CH, and CH (formaldehyde, acetaldehyde, and propionaldehyde, respectively), have been studied using a laser flash-photolysis transient absorption spectroscopy technique. The experimental measurements are supported by calculations at various composite levels of theory that characterize stationary points on the reaction potential and free energy surfaces. As with other reactions of CHOO 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: () = (7.1 ± 1.5) × 10exp((1160 ± 60)/), (8.9 ± 1.7) × 10exp((1530 ± 60)/), and (5.3 ± 1.3) × 10exp((1210 ± 70)/) cm s for HCHO, CHCHO, and CHCHO, respectively. Based on estimated concentrations of CHOO, the reactions with aldehydes are unlikely to play a significant role in the atmosphere.