Mechanisms and kinetics of reaction CHClBr • +NO 2

The reaction CHClBr • +NO 2 was investigated via quantum chemical methods and kinetic calculations. The reaction mechanism on the singlet potential energy surface(PES) was considered by B3LYP method, and the energies were calculated at the CCSD(T) and CASPT2 levels of theory. The rate constants and the ratios of products were obtained by utilizing VTST and RRKM methods over wide temperature and pressure ranges. Our results indicate that carbon-to-nitrogen approach via a barrierless process is preferred in the initial association of CHClBr • and NO 2 . The dominant product is BrNO+CHClO(P 1 ), which agrees well with the experimental observation. P 2 (ClNO+CHBrO) and P 3 (HNO+CBrClO) may also have minor contributions to the reaction. The calculated overall rate constants are independent of pressure and consistent with the experimental data, which can be fitted with the following equation over the temperature range of 200—1500 K: k ( T )=2.31×10 –15 T 0.99 exp(771/ T ). Compared with reaction CH 2 Br • +NO 2 , reaction CHClBr • +NO 2