Experimental and theoretical study of the recombination reaction F + FC(O)O + M → FC(O)OF + M

Abstract

The kinetics of the F + FC(O)O + M → FC(O)OF + M recombination reaction (1) has been experimental and theoretically investigated. Both F atoms and FC(O)O radicals were generated by 193-nm laser flash photolysis of FC(O)OO(O)CF in mixtures with He or CF₄ at 295 K. From the extrapolation of the fall-off curves measured from 55 to 790 Torr total pressure, the high pressure rate coefficient (2.1 ± 0.3) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ and the low pressure rate coefficients (1.6 ± 0.3) × 10⁻²⁹[He], (3.3 ± 0.7) × 10⁻²⁹[CF₄] and (7.1 ± 1.5) × 10⁻²⁹[FC(O)OO(O)CF] cm³ molecule⁻¹ s⁻¹ were determined. The rate coefficient for the reaction between F atoms and FC(O)OO(O)CF has been found to be (1.5 ± 0.5) × 10⁻¹⁵ cm³ molecule⁻¹ s⁻¹. The limiting rate coefficients were analyzed using the unimolecular reaction theory on an ab initio potential energy surface derived at the G3S level of theory. Structural properties, harmonic vibrational frequencies and heats of formation for the FC(O)O radical and for the cis and trans conformers of FC(O)OF calculated with the B3LYP/6-311+G(3df) functional are presented. The values −87.9, −103.4 and −104.6 kcal mol⁻¹, respectively, for the heats of formation of the three molecules were obtained at 298 K from isodesmic energies computed at the G3//B3LYP/6-311++G(3df,3pd) level.