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 mu s, 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 gaucheCF(2)ICF(2).All the nascent gauche-CF2ICF2 radicals reacted with the dissociated I atom within the solvent cage to produce a complex, I-2 center dot center dot C2F4, in <1 ps. The quasi-stable I-2 center dot center dot C2F4 complex in CCl4 (CH3CN or CD3OH) further dissociated into I-2 and C2F4 with a time constant of 180 +/- 5 (46 +/- 3) ps. Some of the anti-CF2ICF2 radicals also formed the I-2 center dot center dot 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 I-2 center dot center dot 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.