Reaction Kinetics of CH₂OO and syn-CH₃CHOO Criegee Intermediates with Acetaldehyde

Criegee intermediates exert a crucial influence on atmospheric chemistry, functioning as powerful oxidants that facilitate the degradation of pollutants, and understanding their reaction kinetics is essential for accurate atmospheric modeling. In this study, the kinetics of CH₂OO and syn-CH₃CHOO reactions with acetaldehyde (CH₃CHO) were investigated using a flash photolysis reaction tube coupled with the OH laser-induced fluorescence (LIF) method. The experimental results indicate that the reaction of syn-CH₃CHOO with CH₃CHO is independent of pressure in the range of 5-50 Torr when using Ar as the bath gas. However, the rate coefficient for the reaction between CH₂OO and CH₃CHO at 5.5 Torr was found to be lower compared to the near-constant values observed between 10 and 100 Torr. Furthermore, the reaction of syn-CH₃CHOO with CH₃CHO demonstrated positive temperature dependence from 283 to 330 K, with a rate coefficient of (2.11 ± 0.45) × 10^-13 cm³ molecule^-1 s^-1 at 298 K. The activation energy and pre-exponential factor derived from the Arrhenius plot for this reaction were determined to be 2.32 ± 0.49 kcal mol^-1 and (1.66 ± 0.61) × 10^-11 cm³ molecule^-1 s^-1, respectively. In comparison, the reaction of CH₂OO with CH₃CHO exhibited negative temperature dependence, with a rate coefficient of (2.16 ± 0.39) × 10^-12 cm³ molecule^-1 s^-1 at 100 Torr and 298 K and an activation energy and a pre-exponential factor of -1.73 ± 0.31 kcal mol^-1 and (1.15 ± 0.21) × 10^-13 cm³ molecule^-1 s^-1, respectively, over the temperature range of 280-333 K.