Probing structural dynamics of five-membered heterocycle with ultrafast electron diffraction

We investigate the structural dynamics of five-membered heterocycle upon the deep UV photoexcitation with a combination of relativistic ultrafast electron diffraction (rUED) and ab-initio multiple spawning simulation (AIMS). We focused this study on 2,3-dihydrofuran (C₄H₆O). Upon absorption of photon in deep UV region (200 nm), the molecule either returns to a vibration hot ground state or ring-opening occurs followed by secondary reactions. Of particular interest with the rUED technique is the structural determination of final products after the molecules relax down to the ground state. We observed real-time structural evolution from the measurements, and detailed comparison between the experiment and AIMS simulation reveals that the molecules undergos ring-opening followed with multiple transient structure formation in a few hundred femtoseconds time scale. The UED experiment offered direct structural information into the relaxation dynamics and provides complementary structural information to our previous time-resolved photoelectron spectroscopy (TRPES) experiment. The combined spectroscopic and structural probes provide new insight into the coupled electronic and nuclear deactivation processes in biologically relevant systems.