Determination of the Temperature Dependence of the Rate Constants for HO2/Acetonylperoxy Reaction and Acetonylperoxy Self-Reaction

Abstract:

Reactions of hydroperoxy radical, HO₂, with carbonyl containing RO₂ can play an important role in the oxidation chemistry of the troposphere. Discovered radical product channels in addition to radical termination channels have resulted in increased study of these important reactions. In our continued study of HO₂ reactions with acetonylperoxy and acetylperoxy radicals, we report here our first results on the kinetics of the acetonylperoxy system. Previous studies have resulted in conflicting results and no temperature dependence of the rate constants. Using the Infrared Kinetic Spectroscopy (IRKS) method in which a temperature-controlled slow-flow tube apparatus and laser flash photolysis of Cl₂ are used to produce HO₂ and CH₃C(O)CH₂O₂ from methanol and acetone, respectively, we studied the chemical kinetics involved over the temperature range of 295 to 240 K. Rates of chemical reaction were determined by monitoring the HO₂ concentration as a function of time by sensitive near-IR diode laser wavelength modulation spectroscopy while simultaneously measuring the disappearance of [CH₃C(O)CH₂O₂] in the ultraviolet at 300 nm. The simultaneous fits resulted in the determination of the temperature dependence of the rate constants for the HO₂/acetonylperoxy reaction and the acetonylperoxy self-reaction. At the lower temperatures, the reactions of HO₂ and CH₃C(O)CH₂O₂ with the adducts HO₂•CH₃OH and HO₂•CH₃C(O)CH₃ formed in significant concentrations needed to be included in the fitting models.