Photolysis of 1,1-Difluoroacetone (CF ₂ HC(O)CH ₃ ) and 1,1,1-Trifluoroacetone (CF ₃ C(O)CH ₃ ): Quantum Yields and Products of UV-B and UV-C Photolysis

The UV-B (broadband 280-320 nm, peak λ = 313 nm) and UV-C (λ = 254 nm) initiated photolytic oxidation of 1,1-difluoroacetone (CF₂HC(O)CH₃) and 1,1,1-trifluoroacetone (CF₃C(O)CH₃) was studied as a function of total pressure using smog chamber techniques. The UV spectrum of CF₂HC(O)CH₃ and CF₃C(O)CH₃ are reported; the former for the first time. The UV-B and UV-C photolysis rates were measured relative to that of CH₃C(O)CH₃. The approximate UV-B (313 nm) quantum yield for CF₂HC(O)CH₃ and CF₃C(O)CH₃ were determined as 0.03 and 0.007. At 254 nm, the overall quantum yields for CF₂HC(O)CH₃ and CF₃C(O)CH₃ were determined as (1.11 ± 0.13) and (0.69 ± 0.08), respectively, at 700 Torr, (298 ± 1) K, independent of diluent gas. This is the first chamber study of the photolysis of CF₂HC(O)CH₃ and CF₃C(O)CH₃. The measured yields of HCOF, COF₂ (and CO) suggest that photolysis of CF₂HC(O)CH₃ and CF₃C(O)CH₃ produces CF₂H and CF₃ radicals, respectively, both in yields of unity. Additional products identified include CH₃OH and HCHO. Pressure-dependent decomposition pathways were identified in the UV-C photolysis and overall photolysis mechanisms are proposed. Finally, the atmospheric photolysis-lifetimes of CF₂HC(O)CH₃ and CF₃C(O)CH₃ were estimated based on a Tropospheric Ultraviolet Visible (TUV) model calculation.