Reaction Mechanisms of C2Cl3 + NO2 via Nitro and Nitrite Adducts

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• 作者：Kunhui Liu ; Tiancheng Xiang ; Weiqiang Wu ; Shaolei Zhao ; Hongmei Su
• 刊名：Journal of Physical Chemistry A
• 出版年：2008
• 出版时间：October 30, 2008
• 年：2008
• 卷：112
• 期：43
• 页码：10807-10815
• 全文大小：260K
• 年卷期：v.112,no.43(October 30, 2008)
• ISSN：1520-5215

文摘

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 preferentially by the N-attack forming nitro adducts (only N-attack is plausible for the C₂H₃ + NO₂ reaction) or the O-attack forming nitrite adducts (O-attack is slightly more favorable and N-attack is also plausible for the C₂Cl₃ + NO₂ reaction). The addition selectivity can be fundamentally correlated to the variation of the charge density of the end carbon atom of the double bond induced by chlorine substitution due to the electron-withdrawing effect of chlorine groups.