Investigation of kinetics and mechanistic insights of the reaction of criegee intermediate (CH2OO) with methyl-ethyl ketone (MEK) under tropospherically relevant conditions

Abstract

The temperature-dependent kinetics was investigated for the reaction of the simplest Criegee intermediate (CH2OO) with Methyl-ethyl ketone (CH3COC2H5, MEK). A direct method was employed to measure the rate of change of the concentration of CH2OO using a highly sensitive Pulsed Laser Photolysis-Cavity Ring-down Spectroscopy (PLP-CRDS) technique. The temperature dependent rate coefficient obtained for the CH2OO + MEK reaction was k4(T = 258–318 K) = (1.26 ± 0.16) × 10−14 × exp{(1179.1 ± 71.8)/T} cm3 molecule−1 s−1 and the rate coefficient at room temperature was k4(298 K) = (6.39 ± 0.20) × 10−13 cm3 molecule−1 s−1 at 50 Torr/N2. Theoretical calculations were performed to predict the reaction mechanism and probable end products. The secondary ozonide (SOZ) formation pathway was found to be the rate determining step, which gets decomposed into HCOOH and MEK as the major products. Both experimental and theoretical results show a negative T-dependency in the studied range.