Reaction Mechanisms of C2Cl3 + NO2 via Nitro and Nitrite Adducts

The atmospherically and environmentally important reaction of chlorinated vinyl radical with nitrogen dioxide (C2Cl3 + NO2) is investigated by step-scan time-resolved Fourier transform infrared emission spectroscopy and electronic structure calculations. Vibrationally excited products of CO, NO, Cl2CO, and NO2 are observed in the IR emission spectra. Geometries of the major intermediates and transition states along the potential energy surface are optimized at the B3LYP/6-311G(d) level, and their energies are refined at the CCSD(T)/ 6-311+G(d) level. The reaction mechanisms are characterized to be barrierless addition-elimination via nitro (C2Cl3-NO2) and nitrite (C2Cl3-ONO) adducts. Four energetically accessible reaction routes are revealed, i.e., the decomposition of the nitrite adduct forming C2Cl3O + NO and its sequential dissociation to CO + NO + CCl3, the elimination of ClNO from the nitrite adduct leading to ClNO + Cl2CCO, the Cl-atom shift of the nitrite adduct followed by the decomposition to CCl3CO + NO, and the O-atom shift of the nitro adduct followed by C-C bond cleavage forming ClCNO + Cl2CO. In competition with these reactive fluxes, the back-decomposition of nitro or nitrite adducts leads to the prompt formation of vibrationally excited NO2 and the long-lived reaction adducts facilitate the vibrational energy transfer. Moreover, the product channels and mechanisms of the C2Cl3 + NO2 reaction are compared with the C2H3 + NO2 reaction to explore the effect of chlorine substitution. It is found that the two reactions mainly differ in the initial addition preferentiall