Direct Kinetic Measurements of a Cyclic Criegee Intermediate; Unimolecular Decomposition of (CH)COO.

We report the first direct kinetic measurements of a cyclic stabilized Criegee Intermediate. We have measured the unimolecular reaction rate coefficient of cyclohexanone oxide ((CH)COO) in the temperature 213-296 K and pressure 7-50 Torr ranges using absorption spectrometry. The (CH)COO was produced by the photolysis of (CH)CIBr at 213 nm in the presence of O. We compare the measured fast (CH)COO unimolecular rate coefficient, 1998 ± 147 s at 296 K, with the literature calculations for the structurally similar -nopinone oxide formed in β-pinene ozonolysis. The ((CH)COO)/(-nopinone oxide) ratio calculated using transition-state theory and density functional theory agrees well with this comparison. We have also measured the bimolecular rate coefficient of the reaction between (CH)COO and trifluoroacetic acid at 253 K and 10 Torr and obtained the value (8.7 ± 1.0) × 10 cm molecule s. This very large value agrees with previous kinetic measurements for reactions between stabilized Criegee intermediates and halogenated organic acids.