Complete Characterization of Photochemical Reactions by Time- and Energy-Resolved Electron Scattering

Many processes in nature and industry are intricately linked to the structure-function relationship of molecules, which optical stimuli can profoundly alter. Chemists and physicists have long sought to unravel the ultrafast structural changes of photochemical reactions. Using two short pulses with precisely synchronized time delays, a series of snapshots of the evolving electronic and molecular structures at various reaction times can be collected, analogous to assembling frames in a video. Measuring coupled electronic-nuclear dynamics remains a formidable challenge due to the small time, energy and spatial scales involved. State-of-the-art ultrafast electron diffraction (UED) techniques excel in molecular structure retrieval, but the critical signatures stemming from simultaneous transformations in electronic structure remain elusive, as several molecular reaction channels overlap and cannot be separated with current imaging technologies.My goal is to pioneer a novel time- and energy-resolved electron scattering (TERES) method for real-time monitoring of coupled electronic-nuclear dynamics in photochemical reactions by energy-resolving UED. TERES will experimentally separate and identify electron scattering signals arising from different electronic structures of excited molecules (e.g., in different excited states) while preserving molecular structure information, comprehensively mapping the potential energy surfaces involved at different reaction times capabilities significantly exceeding current UED technology. Successful realization of TERES promises to usher in a new era in photochemistry, unveiling hidden aspects of chemical reactivity.