We have investigated the structural dynamics in photoexcited 1,2-diiodotetrafluoroethane molecules in the gas phase experimentally using ultrafast electron diffraction and theoretically using FOMO-CASCI excited-state dynamics simulations. The molecules are excited by an ultraviolet femtosecond laser pulse to a state characterized by a transition from the iodine orbital to a mixed hole and antibonding orbital, which results in the cleavage of one of the carbon-iodine bonds. We have observed, with sub-Angstrom resolution, the motion of the nuclear wave packet of the dissociating iodine atom followed by coherent vibrations in the electronic ground state of the radical. The radical reaches a stable classical (nonbridged) structure in less than 200 fs.