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.