Kinetics and Mechanism of the OH Radicals-Initiated Oxidation of 3-Methyl-3-penten-2-one in the Atmosphere

Abstract

The 3-methyl-3-penten-2-one (3M3P2) reaction with OH radicals was studied in theoretical calculations based on QCISD(T)//BH&HLYP quantum chemistry results. The rate coefficients for the OH radical reaction with 3M3P2 were obtained with the conventional transition state theory including Eckart tunneling corrections. The room-temperature rate coefficient k was found to be 6.01 × 10^–11 cm³ molecule^–1 s^–1, which is aligned to the experimental result. The rate coefficient over the temperature range 260–400 K can be approximated by a modified Arrhenius expression k (T) = 4.00 × 10^–18 × T^1.8 × exp(1870.7/T) cm³ molecule^–1 s^–1. The calculated rate coefficient shows a negative temperature dependence at the temperatures ranging from 260 to 400 K. The kinetics was governed by the formation of two addition intermediates. Under atmospheric conditions, these two intermediates can react with O₂/NO_x to produce acetaldehyde, biacetyl (2,3-butanedione), acetoin (3-hydroxy-2-butanone), CO₂, and peroxyacetyl nitrate (PAN) as the predominant products, which is in line with the experimental observations. A reasonable reaction mechanism for the OH radical reaction with 3M3P2 in the atmosphere is proposed, and the atmospheric implications are also discussed.