Detailed kinetics of tetrafluoroethene ozonolysis

Abstract

The C₂F₄ + O₃ reaction plays an important role in the oxidation process of perfluoroalkenes in the atmosphere. The detailed reaction mechanism was explored using the accurate electronic structure method, CCSD(T)/CBS//B3LYP/aug-cc-pVTZ. The 1,3-cycloaddition of O₃ with C₂F₄ to form the primary ozonide was found to be the rate-determining step of the oxidation process with a small barrier (i.e., 7.3 kcal mol⁻¹ at 0 K). The temperature- and pressure-dependent behaviors of the title reaction were characterized in the range of 200–1000 K & 0.1–760 Torr using the integrated deterministic and stochastic master equation/Rice–Ramsperger–Kassel–Marcus (ME/RRKM) rate model with the inclusion of the corrections for anharmonicity and tunneling treatments. It is found that the anharmonic effect plays a role in the kinetic behaviors (e.g., lower the rate by a factor of ∼ two at 298 K) while the tunneling correction is insignificant. The total rate constants were found to be pressure-independent under the considered conditions, shown as k_tot(T) = 4.80 × 10⁻²³ × T^2.69 × exp(−2983.4 K/T) (cm³ per molecule per s), which confirms the latest experimental data by Acerboni et al. (G. Acerboni, N. R. Jensen, B. Rindone and J. Hjorth, Chem. Phys. Lett., 1999, 309, 364–368); thus this study helps to resolve a long-term controversy among the previous measurements. The sensitivity analyses on the derived rate coefficients and time-resolved species mole fraction with respect to the ab initio input parameters were also performed to further understand as well as quantify the kinetic behaviors for the title reaction.