Diffractive imaging of dissociation and ground-state dynamics in a complex molecule

Abstract

We have investigated the structural dynamics in photoexcited 1,2-diiodotetrafluoroethane molecules $({\mathrm{C}}_{2}{\mathrm{F}}_{4}{\mathrm{I}}_{2})$ 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 $5p\ensuremath{\perp}$ orbital to a mixed $5p\ensuremath{\parallel}\ensuremath{\sigma}$ hole and ${\mathrm{CF}}_{2}^{\ifmmode\bullet\else\textbullet\fi{}}$ 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 ${\mathrm{C}}_{2}{\mathrm{F}}_{4}\mathrm{I}$ radical. The radical reaches a stable classical (nonbridged) structure in less than 200 fs.