Thermochemistry of Species in Gas-Phase Thermal Oxidation of C 2 to C 8 Perfluorinated Carboxylic Acids.

New thermochemical properties, C p ° ( T ), H °( T ), S °( T ), and G °( T ), are predicted for 123 species involved in the thermal destruction of perfluorinated carboxylic acids (PFCAs) using computational quantum chemistry and ideal-gas statistical mechanics. Relevant species were identified from the development of mechanisms for the pyrolysis and oxidation of PFCAs of C 2 to C 8 in length. Partition functions were obtained from the results of calculations at the G4 level for species up to C 4 in length and M06-2X-D3(0)/def2-QZVPP for species C 5 to C 8 in length. The 1D hindered-rotor approximation was used to correct for torsional modes in the larger species. Ideal-gas thermochemistry was computed and fitted to 7-parameter NASA polynomials over a 200-2500 K temperature range, and the data are provided in standardized format. To gauge the effects of both method and basis set choice, enthalpies of formation at 0 K are calculated from various other density functionals (including B3LYP and ωB97XD), basis sets, and composite model chemistries (CBS-QB3). They are benchmarked against data from the Active Thermochemical Tables, high-level ANL0 calculations from the literature, and G4 calculations from this work. The effects of internal rotations and other anharmonicities are discussed, and bond dissociation energies and reaction equilibria provide mechanistic insights.