Research

1. Gas-phase Ultrafast Electron Diffraction (GUED)


GUED unveils non-adiabatic dynamics in photoexcited small molecules

MeV-GUED employs relativistic electron beam to probe the structure of molecules on their natural time scale (femtoseconds) and length scale (sub-angstrom). By recording time-resolved diffraction patterns we can track the evolution of molecular structure in real time and thus make molecular movies.

In this direction, we will study the photophysics and photochemistry of small molecules in the gas phase using MeV-GUED. These experiments will be carried out in collaboration with Prof. Renkai Li from Department of Engineering Physics, Tsinghua University and Prof. Dao Xiang from Department of Physics, Shanghai Jiaotong University.

Selected publications in GUED:

2. Liquid-phase Ultrafast Electron Diffraction (LUED)

LUED employs microfluidic chips for making ultrathin liquid sheet in vacuum

The study of photo-induced molecular dynamics in solutions and bulk liquids by electron diffraction requires a sample thickness on the order of 100 nm in vacuum. This type of ultra-thin liquid sheet can be produced using gas-accelerated liquid jet technology (Koralek et al., Nat. Commun. 2018, 9, 1353). By combining such liquid jet technology with a relativistic electron source, we built a novel instrument that has enabled MeV-UED measurements on liquid phase samples for the first time. In this project, we will study the structural relaxation of solvent molecules under non-equilibrium conditions, the coupling between intermolecular and intramolecular degrees of freedoms through, for example, hydrogen bond networks, and provide experimental benchmarks for MD simulations.

Selected Publications in LUED:

3. Time-resolved photoelectron spectroscopy (TRPES)

Image credit: Yusong Liu/Stony Brook University

TRPES is a pump-probe spectroscopic method that is able to trace electronic configuration and energy relaxation of photoexcited molecules on femtosecond timescales. We will set up a UV-pump VUV-probe experimental scheme. The photoelectron and/or photoion will be detected using a velocity map imaging detector. TRPES and MeV-UED are two complementary experimental methods: TRPES are mostly sensitive to valence electronic dynamics, while MeV-UED are mostly sensitive to nuclear structural dynamics. We will focus on unveiling the complex electronic-nuclear interplay in nonadiabatic dynamics by combining the two experimental techniques.