Mechanism and kinetic study on the degradation of unsaturated esters initiated by OH radical

Abstract

Unsaturated esters are volatile organic pollutants. The widespread use of them will unavoidably result in the fugitive emission of pollutants into the atmosphere. In order to evaluate the fate of unsaturated esters in the atmosphere, a dual-level direct dynamics study on the degradation mechanisms of three kinds of unsaturated esters initiated by OH radical is carried out. The equilibrium geometries and the corresponding harmonic vibrational frequencies of the stationary points are obtained at the M06-2X/6-311++G(d,p) level, and the energetic information are further refined at M06-2X/6-311++G(3df,2p) level. The rate constants of the twenty-four reaction channels are calculated by the improved canonical variational transition state theory with small-curvature tunneling correction over the temperature range 200–1000 K. The total rate constants are in good agreement with the available experimental values. Besides, the three-parameter expressions of the total rate constants k a (T) = 7.00 × 10−19 T 2.66 exp(953.32/T), k b (T) = 2.29 × 10−22 T 3.98 exp(1040.29/T), k c (T) = 1.19 × 10−17 T 2.42 exp(101.99/T) cm3 mol−1 s−1 are given. Our results indicate that the addition reaction on the carbon–carbon double bond is major reaction channel. This study can provide a detailed knowledge of the preliminary degradation of unsaturated esters initiated by OH radical.