Time-Resolved Structural Studies of Reacting Molecules Using Stroboscopic Gas Electron Diffraction Synchronous with Photoexcitation

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In this project in the Physical Chemistry Program of the Chemistry Division, Professors J. Ewbank and L. Schafer of the Chemistry Department of the University of Arkansas will continue to apply stroboscopic diffraction techniques to the structural dynamics of chemical reactions. Laser-excited molecules in the vapor phase will be studied using time-resolved electron scattering in order to provide information about the time evolution of structures and vibrational probability distributions in reacting molecules. The time resolution will be extended down to the picosecond time domain and will be used to study UV-induced isomerizations of unsaturated organic compounds such as trans-stilbene, and structural and distribution dynamics following IR multiphoton absorption-induced processes such as intramolecular vibrational energy redistribution and dissociation reactions. Experimental observations of the structural kinetics of energized molecules in non-equilibrium distributions are an important chemical frontier which will stimulate advances in theory. Traditional gas electron diffraction (GED) has relied on the use of the photographic plate to record and store the information generated by the diffraction of electrons by molecules. This method was therefore limited to studying the structures of stable molecules. Current research in molecular dynamics concerns itself with how the structure and conformation of a molecular system evolves during a chemical reaction. Experimental information about such processes can be obtained only by means of techniques in which the time plays an essential role. The method of real-time GED developed by the principal investigators has shown great promise in making important contribution to the understanding of the properties of short-lived species. The aim of this project is to capitalize on this potential and contribute to our understanding of the basic aspects of molecular dynamics.