Gas-Phase Reaction between CF₂O and CF₃C(O)OH: Characterization of CF₃C(O)OC(O)F

Area of Science:

• Atmospheric Chemistry
• Chemical Kinetics
• Molecular Spectroscopy

Background:

• Trifluoroacetic acid and carbonyl fluoride (CF2O) are significant in atmospheric hydrochlorofluorocarbon oxidation.
• Understanding their thermal decomposition is crucial for atmospheric modeling.

Purpose of the Study:

• To investigate the thermal reaction mechanism between trifluoroacetic acid and carbonyl fluoride (CF2O).
• To characterize reaction intermediates and products.
• To determine kinetic parameters and activation energy.

Main Methods:

• Fourier transform infrared spectroscopy (FTIR) in the temperature range of 513-573 K.
• First-principles calculations at the G4MP2 level of theory.

Main Results:

• Identified a novel reaction intermediate, CF3C(O)OC(O)F.
• Major products: CF3C(O)F, HF, and CO2.
• Reaction kinetics: first-order in each reagent, second-order overall, with Ea = 110.1 ± 6.1 kJ mol⁻¹.
• Calculated thermodynamic activation values: ΔH‡ = 105.6 ± 6.4 kJ mol⁻¹, ΔS‡ = -88.6 ± 9.7 J mol⁻¹ K⁻¹, ΔG‡ = 153.7 ± 13.5 kJ mol⁻¹.

Conclusions:

• The reaction proceeds via a two-step mechanism, with the first step being rate-determining.
• Low activation energy attributed to hydrogen-bond interactions.
• Excellent agreement between experimental and theoretical results validates the proposed mechanism.