A theoretical investigation on the kinetics and reactivity of the gas-phase reactions of ethyl chlorodifluoroacetate with OH radical and Cl atom at 298 K

摘要

The mechanism, kinetics, and thermochemistry of the gas-phase reactions of CF_2ClC(O)OCH_2CH_3,ethyl chlorodifluoroacetate (ECDFA) with the OH radical and Cl atom are investigated. Geometry optimization and frequency calculations have been performed at the MPWB1K/ 6-31?G(d,p) level of theory and energetic information is refined by using G2(MP2) theory. Transition states are searched on the potential energy surface of reaction channels and each of the transition states is characterized by the presence of only one imaginary frequency. Connections of the transition states between designated local minima are confirmed by intrinsic reaction coordinate calculation. Theoretically calculated rate constants at 298 K using the Canonical Transition State Theory are found to be in good agreement with the experimentally measured ones. Using group-balanced isodesmic reactions as working chemical reactions, the standard enthalpies of formation for CF_2ClC(O)OCH_2CH_3, CF_2ClC(O)OCH_2CH_2, and CF_3C(O) OCHCH_3 are also reported for the first time. The hydrogen abstraction occurs mainly from -CH_2 group. The T1 diagnostic calculation suggests that the multi-reference character is not an issue for such systems. The estimated atmospheric life time of ECDFA is expected to be around 24 days.