Theoretical investigation on mechanism, kinetics and thermochemistry of gas-phase reactions of ethyl trifluoroacetate with OH radicals

• Reactions between CF3C(O)OCH2CH3 with OH radicals were investigated.
• Two conformers are identified and taken into account for kinetic study.
• The indirect mechanism has been proposed.
• Thermochemistry including BDE (D0) and ΔfH0 were also reported.

The reaction mechanism of OH-initiated hydrogen abstraction reactions of CF3C(O)OCH2CH3, ethyl trifluoroacetate (ETFA) were investigated by performing DFT calculations. The optimized geometries, frequencies and minimum energy path were obtained at MPWB1K in conjunction with 6-31+G(d,p) basis set. The single-point energy calculations were further refined by using high level G2(MP2) method. Two conformers of ETFA have been located and considered for kinetic calculations. The rate constants of the two reactions are determined for the first time in a wide temperature range of 200–450 K. The evaluated rate constant (2.43 × 10−13) at 298 K is found to be in good agreement with the available experimental data [(2.64 ± 0.59) × 10−13]. The standard enthalpies of formation for species are evaluated by using a series of isodesmic reactions. The OH-driven atmospheric life time are also estimated and compared with literature values. Based on mechanistic and kinetics studies, we suggest that the H abstraction from CH2 group is more favorable than the CH3 group.

Relative energy diagram for SC1 + OH reactions calculated at G2(MP2) and MPWB1K (within parenthesis) levels of theory. All values are in kcal mol−1.Figure optionsDownload as PowerPoint slide