Photodissociation dynamics of CF₃CHO: C–C bond cleavage

The photodissociation dynamics of jet-cooled trifluoroacetaldehyde (CF₃CHO) into radical products, CF₃ + HCO, was explored using velocity mapped ion imaging over the wavelength range 297.5 nm $≤λ≤$ 342.8 nm (33 613–29 172 cm⁻¹) covering the entire section of the absorption spectrum accessible with solar actinic wavelengths at the ground level. After initial excitation to the first excited singlet state, S₁, the radical dissociation proceeds largely via the first excited triplet state, T₁, at excitation energies above the T₁ barrier. By combining velocity-mapped ion imaging with high-level theory, we place this barrier at 368.3 ± 2.4 kJ mol⁻¹ (30 780 ± 200 cm⁻¹). After exciting to S₁ at energies below this barrier, the dissociation proceeds exclusively via the ground electronic state, S₀. The dissociation threshold is determined to be 335.7 ± 1.8 kJ mol⁻¹ (28 060 ± 150 cm⁻¹). Using laser-induced fluorescence spectroscopy, the origin of the S₁ ← S₀ transition is assigned at 28 903 cm⁻¹. The S₀ dissociation channel is active at the S₁ origin, but the yield significantly increases above 29 100 cm⁻¹ due to enhanced intersystem crossing or internal conversion.