An experimental and computational study of the unimolecular-decay reaction of diethyl-substituted Criegee intermediate (C2H5)2COO.

Abstract

We have performed direct kinetic measurements to determine the thermal unimolecular-decay rate coefficient of (C2H5)2COO as a function of temperature (223-296 K) and pressure (4-100 torr) using time-resolved UV-absorption spectroscopy. The stabilised (C2H5)2COO Criegee intermediate was produced by photolysing 3-bromo-3-iodopentane ((C2H5)2CIBr) with 213 nm radiation in the presence of O2. We performed quantum-chemistry calculations and master-equation simulations to complement the experimental work. At 296 K and 100 torr, we measure 1530 ± 440 s-1 (2σ) for the unimolecular-decay rate coefficient, and both the experiments and simulations indicate that the reaction is effectively at the high-pressure limit under these conditions. Key parameters in the master-equation model were optimised using the experimental results, and phenomenological rate coefficients were then computed to facilitate the use of the present results in modelling. A roaming channel that forms (R/S)-2-hydroxypentan-3-one was included in the master-equation model. We also performed similar calculations for the unimolecular-decay reaction of (CH3)2COO to improve the kinetic modelling of our previous work [J. Peltola et al., Phys. Chem. Chem. Phys., 2022, 24, 5211-5219].