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

TL;DR

This study combines ultrafast electron diffraction experiments and theoretical simulations to observe real-time molecular dissociation and ground state dynamics in photoexcited C2F4I2 molecules, revealing sub-angstrom nuclear motions and rapid stabilization.

Contribution

It provides the first combined experimental and theoretical analysis of ultrafast dissociation and vibrational dynamics in a complex molecule with sub-angstrom resolution.

Findings

Observation of iodine atom dissociation dynamics

Detection of coherent vibrations in the ground state

Radical stabilization within 200 femtoseconds

Abstract

We have investigated the structural dynamics in photoexcited 1,2-diiodotetrafluoroethane molecules (C2F4I2) in the gas phase experimentally using ultrafast electron diffraction and theoretically using FOMO-CASCI excited state dynamics simulations. The molecules are excited by an ultra-violet femtosecond laser pulse to a state characterized by a transition from the iodine 5p orbital to a mixed 5p|| hole and CF2 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 wavepacket of the dissociating iodine atom followed by coherent vibrations in the electronic ground state of the C2F4I radical. The radical reaches a stable classical (non-bridged) structure in less than 200 fs.