Conformer-Specific Photodissociation Dynamics of CF₂ICF₂I in Solution Probed by Time-Resolved Infrared Spectroscopy

The photodissociation dynamics of CF₂ICF₂I in solution was investigated from 0.3 ps to 100 μs, after the excitation of CF₂ICF₂I with a femtosecond UV pulse. Upon excitation, one I atom is eliminated within 0.3 ps, producing a haloethyl radical having a classical structure: anti-CF₂ICF₂ and gauche-CF₂ICF₂. All the nascent gauche-CF₂ICF₂ radicals reacted with the dissociated I atom within the solvent cage to produce a complex, I₂··C₂F₄, in <1 ps. The quasi-stable I₂··C₂F₄ complex in CCl₄ (CH₃CN or CD₃OH) further dissociated into I₂ and C₂F₄ with a time constant of 180 ± 5 (46 ± 3) ps. Some of the anti-CF₂ICF₂ radicals also formed the I₂··C₂F₄ complex with a time constant of 1.5 ± 0.3 ps, while the remaining radicals underwent secondary elimination of I atom in a few nanoseconds. The time constant for the secondary dissociation of I atom from the anti-CF₂ICF₂ radical was independent of the excitation wavelength, indicating that the excess energy in the nascent radical is relaxed and that the secondary dissociation proceeds thermally. The formation of the I₂··C₂F₄ complex and the thermal dissociation of the anti-CF₂ICF₂ radical clearly demonstrate that even a weakly interacting solvent plays a significant role in the modification and creation of reaction.