Journal Article

Imaging CF3I conical intersection and photodissociation dynamics with ultrafast electron diffraction

Weathersby, Stephen, Li, Zheng, Zhu, Xiaolei, Nunes J Pedro F, Wilkin, Kyle J, Wolf Thomas J A, Gühr Markus, Yoneda, Charles, Veccione Theodore, Coffee, Ryan, Shen Xiaozhe, Martinez, Todd J, Centurion, Martin, Heinz, Tony F, Cryan, James P, Zheng, Qiang, Yang, Jie, Hegazy Kareem, Wang, Xijie, Jobe, Keith, Li Renkai

2018

Overview

Motion picture of a conical intersectionIn most chemical reactions, electrons move earlier and faster than nuclei. It is therefore common to model reactions by using potential energy surfaces that depict nuclear motion in a particular electronic state. However, in certain cases, two such surfaces connect in a conical intersection that mingles ultrafast electronic and nuclear rearrangements. Yang et al. used electron diffraction to obtain time-resolved images of CF3I molecules traversing a conical intersection in the course of photolytic cleavage of the C–I bond (see the Perspective by Fielding).Science, this issue p. 64; see also p. 30Conical intersections play a critical role in excited-state dynamics of polyatomic molecules because they govern the reaction pathways of many nonadiabatic processes. However, ultrafast probes have lacked sufficient spatial resolution to image wave-packet trajectories through these intersections directly. Here, we present the simultaneous experimental characterization of one-photon and two-photon excitation channels in isolated CF3I molecules using ultrafast gas-phase electron diffraction. In the two-photon channel, we have mapped out the real-space trajectories of a coherent nuclear wave packet, which bifurcates onto two potential energy surfaces when passing through a conical intersection. In the one-photon channel, we have resolved excitation of both the umbrella and the breathing vibrational modes in the CF3 fragment in multiple nuclear dimensions. These findings benchmark and validate ab initio nonadiabatic dynamics calculations.

• Publisher: The American Association for the Advancement of Science
• Subject: Bifurcations / Chemical reactions / Diffraction / Electron diffraction / Electron states / Electrons / Excitation / Intersections / Molecular chains / Nuclear reactions / Nuclei / Nuclei (nuclear physics) / Organic chemistry / Photodissociation / Polyatomic molecules / Potential energy / Spatial discrimination / Spatial resolution / Trajectories