Theoretical study on the kinetics of the reaction CH₂Br + NO₂.

Abstract

The mechanism for the reaction CH2Br + NO2 was investigated by quantum chemical calculation, and the kinetic calculations were carried out by means of multichannel RRKM and variational transition-state theory method. Both singlet and triplet potential energy surfaces (PESs) were considered at the CCSD(T)/6-311++G(d,p)//B3LYP/6-311G(d,p) level. The results show that the singlet PES is preferred, and the initial association is a barrierless process (CH2Br + NO2 → CH2BrNO2), consistent with previous study, while the reaction occurring on the triplet PES is unfavorable due to the high barriers at the entrance channels. The calculated overall rate constants agree well with the experimental data within the measured temperature range of 221-363 K, fitted to the expression of k(T) = 2.61 × 10(-10)T(-0.76) exp(461/T) cm(3) molecule(-1) s(-1) over the temperature range of 200-2000 K. The product ratios were obtained by using master equation modeling and show that the formation of product CH2O + BrNO (P1) is dominant, in line with the experimental observation.