Theoretical Investigation of the Reactions of CF3CHFOCF3 with the OH Radical and Cl Atom

A dual-level direct dynamic method is employed to study the reaction mechanisms of CF3CHFOCF3 (HFE-227 mc) with the OH radical and Cl atom. The geometries and frequencies of all the stationary points and the minimum energy paths (MEPs) are calculated at the BH&H-LYP/6-311G(d,p) level, and the energetic information along the MEPs is further refined by MC-QCISD theory. The classical energy profile is corrected by the interpolated single-point energies (ISPE) approach, incorporating the small-curvature tunneling effect (SCT) Calculated by the variational transition state theory (VTST). The rate constants are in good agreement with the experimental data and are found to be k(1) = 2.87 x 10(-21)T(2.80) exp(-1328.60/7) and k(2) = 3.26 x 10(-16)T(1.65) exp(-4642.76/T) cm(3) molecule(-1) s(-1) over the temperature range 220-2000 K. The standard enthalpies of formation for the reactant CF3CHFOCF3 and product radical CF3CFOCF3 are evaluated via group-balanced isodesmic reactions, and the corresponding values are -454.06 +/- 0.2 and -402.74 +/- 0.2 kcal/mol, respectively, evaluated by MC-QCISD theory based on the BH&H-LYP/6-311G(d, p) geometries. The theoretical studies provide rate constants of the title reactions and the enthalpies of formation of the species, which are important parameters in determining the atmospheric lifetime and the feasible pathways for the loss of HFE-227 mc.