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

The photodissociation dynamics of CFICFI in solution was investigated from 0.3 ps to 100 μs, after the excitation of CFICFI with a femtosecond UV pulse. Upon excitation, one I atom is eliminated within 0.3 ps, producing a haloethyl radical having a classical structure: -CFICF and -CFICF. All the nascent -CFICF radicals reacted with the dissociated I atom within the solvent cage to produce a complex, I··CF, in <1 ps. The quasi-stable I··CF complex in CCl (CHCN or CDOH) further dissociated into I and CF with a time constant of 180 ± 5 (46 ± 3) ps. Some of the -CFICF radicals also formed the I··CF 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 -CFICF 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··CF complex and the thermal dissociation of the -CFICF radical clearly demonstrate that even a weakly interacting solvent plays a significant role in the modification and creation of reaction.