Theoretical study on the reaction mechanism of carbaryl with OH radicals.

A theoretical investigation on the multiple-channel degradation mechanism of carbaryl with ·OH in the atmosphere was completed by the variational transition state theory. Eleven reaction channels have been identified using the density functional theory. The equilibrium geometries and the corresponding harmonic vibrational frequencies of the stationary points were obtained at the B3LYP/6-31++G(d,p) level. The minimum energy paths were calculated at the same level, and energetic information was further refined at the B3LYP/6-31++G(3df,2p) level. The rate constants of the 11 reaction channels were calculated by improved canonical variational transition state theory with small-curvature tunneling correction over the temperature range 200-800 K. The total rate constants are in good agreement with available experimental data and the three-parameter expression k(T) = 1.85 × 10(-21)  T (3.44)exp(1180.18/T) cm(3) molecule(-1) s(-1) was given.