Direct kinetic measurements are reported for the self-reaction and unimolecular decay of methyl vinyl ketone oxide (MVKOO), and its reactions with trifluoroacetic acid (TFA) and formic acid (FA). The syn-MVKOO stabilized Criegee intermediate was generated by laser flash photolysis of 1,3-diiodobut-2-ene in excess O2 and monitored via its absorption at 360 nm using cavity ring-down spectroscopy. Time-resolved MVKOO decay traces recorded in the absence of added coreactants were analyzed to separate the first-order unimolecular thermal decomposition from second-order self-reaction contributions. Within the 270–330 K temperature and 40–200 Torr pressure ranges studied, MVKOO undergoes rapid second-order self-reaction with a rate coefficient kSR = (12 ± 4) × 10–10 cm3 s–1 that shows no significant temperature or pressure dependence. At 292 K, the unimolecular decay rate coefficient is kuni = (50 ± 21) s–1, averaged over 40–200 Torr measurements, and shows a positive temperature dependence. Bimolecular reactions of MVKOO with FA and TFA were investigated under pseudo-first-order conditions, yielding rate coefficients of kFA = (1.9 ± 0.2) × 10–10 cm3 s–1 and kTFA = (3.8 ± 0.3) × 10–10 cm3 s–1 at 292 K, respectively. The MVKOO + TFA reaction exhibits a weak negative temperature dependence. The measured rate coefficients for MVKOO reaction with FA and TFA are consistent with the predictions from a structure–activity relationship based on dipole-mediated interactions. These findings quantify key unimolecular and bimolecular loss processes of MVKOO and further highlight the potential atmospheric significance of Criegee intermediate–acid chemistry in organic oxidation pathways.
Khodia et al. (Wed,) studied this question.