Theoretical Studies On The Mechanism And Kinetics Of The CH₃CH₂C(O)OCH₂CH₃+OH Reaction

Volatile organic compounds(VOCs) are considered as very important research objects in theoretical chemistry, for their reactions in the atmosphere have a significant impact on environmental, especially the urban photochemical smog contributed by the atmospheric oxidation of VOCs. Some esters belong to VOCs, and are used as solvents in industry. Due to the increasing use of biofuel, some short chain esters were detected during the combustion of biofuels, which caused great concerns. The main atmospheric reactions of esters are the oxidation initiated by OH radical, so, in order to assess the environmental impact of esters, a detailed study of the oxidation mechanism as well as accurate kinetic data is required.In this paper, we focous on the CH₃CH₂C(O)OCH₂CH₃ + OH reaction. CH₃CH₂C(O)OCH₂CH₃ is an important member of short chain esters, which has a representative kinetic mechanism. The CH₃CH₂C(O)OCH₂CH₃ + OH reaction has more than one reaction H-abstraction channels, all the stationary points were optimized and their frequencies were obtained by the M06-2x/aug-cc-pVDZ method, and the single-point energies of the stationary and nonstationary points were refined at the MCG3-MPWB level. The rate constants of the CH₃CH₂C(O)OCH₂CH₃ + OH reaction were calculated by using improved canonical transition-state theory with small-curvature tunneling correction (ICVT/SCT) with interpolated single-point energies (ISPE), over the temperature range 200-2000 K. A negative temperature dependence of rate constants was comfirmed at the temperature below 500 K, the branching ratios of each channel indicate that the hydrogen abstraction from the -CH₂- group (R4) of the alkoxy end of the molecule CH₃CH₂C(O)OCH₂CH₃ is the dominant channel for the CH₃CH₂C(O)OCH₂CH₃ + OH reaction at low temperature range, while as the temperature increases, the contributions to the overall reaction from the other H-abstraction channels increase gradually; the calculated overall rate constants k_T were in good agreement with experimental data, especially with the values by Cometto et al. in the range of 243-372 K. In addition, to provide a reference for future research, the four-parameter rate-temperature expression for the rate constants (k_T) within 200-2000 K is fixed.