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Computational study of H-abstraction reactions from CH3OCH2CH2Cl/CH3CH2OCH2CH2Cl by Cl atom and OH radical and fate of alkoxy radicals

Ye, Jin-Ting, Bai, Feng-Yang, Pan, Xiu-Mei
Environmental science and pollution research international 2016 v.23 no.23 pp. 23467-23484
chemical bonding, chlorine, enthalpy, free radicals, gases, global warming, hydrogen, hydroxyl radicals, oxygen, ozone, superoxide anion
Multichannel gas-phase reactions of CH₃OCH₂CH₂Cl/CH₃CH₂OCH₂CH₂Cl with chlorine atom and hydroxyl radical have been investigated using ab initio method and canonical variational transition-state dynamic computations with the small-curvature tunneling correction. Further energetic information is refined by the coupled-cluster calculations with single and double excitations (CCSD)(T) method. Both hydrogen abstraction and displacement processes are carried out at the same level. Our results reveal that H-abstraction from the –OCH₂– group is the dominant channel for CH₃OCH₂CH₂Cl by OH radical or Cl atom, and from α-CH₂ of the group CH₃CH₂– is predominate for the reaction CH₃CH₂OCH₂CH₂Cl with Cl/OH. The contribution of displacement processes may be unimportant due to the high barriers. The values of the calculated rate constants reproduce remarkably well the available experiment data. Standard enthalpies of formation for reactants and product radicals are calculated by isodesmic reactions. The Arrhenius expressions are given within 220–1200 K. The atmospheric lifetime, ozone depleting potential (ODP), ozone formation potential (OFP), and global warming potential (GWP) of CH₃OCH₂CH₂Cl/CH₃CH₂OCH₂CH₂Cl are investigated. Meanwhile, the atmospheric fate of the alkoxy radicals are also researched using the same level of theory. To shed light on the atmospheric degradation, a mechanistic study is obtained, which indicates that reaction with O₂ is the dominant path for the decomposition of CH₃OCH(O•)CH₂Cl, the C–C bond scission reaction is the primary reaction path in the consumption of CH₃CH(O•)OCH₂CH₂Cl in the atmosphere. HIGHLIGHTS: Ab initio method and canonical variational transition-state theory are employed to study the kinetic nature of hydrogen abstraction reactions of CH₃OCH₂CH₂Cl/CH₃CH₂OCH₂CH₂Cl with Cl atom and OH radical and fate of alkoxy radicals (CH₃OCH(O•)CH₂Cl/CH₃CH(O•)OCH₂CH₂Cl).