Theoretical studies and rate constant calculations of the reactions C₂F₅CHO with OH radicals and Cl atoms

The hydrogen abstraction reactions of C₂F₅CHO with OH radicals and Cl atoms have been investigated theoretically by a dual-level direct dynamics method. In this study, the optimized geometries and frequencies of the stationary points are calculated at the MP2/cc-pVDZ level of theory. The energies of the stationery points and the selected points along the minimum energy paths are further refined at the MC-QCISD level using the MP2 geometries. Complexes with energies less than those of the reactants or products are located at the entrance or the exit channels of the two reactions. This result indicates that both of reactions proceed via indirect reaction mechanisms. The enthalpies of formation for the reactant C₂F₅CHO and the product radical C₂F₅CO are estimated by isodesmic reactions at the MC-QCISD//MP2/cc-pVDZ level. At the same level, the rate constants are calculated by canonical variational transition state theory (CVT) incorporating with the small-curvature tunneling correction (SCT) in the temperature range 200-1000 K. Good agreement between the calculated and experimental rate constants is obtained at the room temperature. Due to the lack of the kinetic data of these reactions, the fitted three-parameter expressions based on the CVT/SCT rate constants within 200-1000 K are k₁ = 1.64 × 10^-24 T^4.33 exp (-566.1/T) and k₂ = 6.33 × 10^-15 T^1.35 exp (550.3/T) cm³ molecule^-1 s^-1, respectively.