Photo- and Radiation Chemistry

The Photo- and Radiation Chemistry program, supported by DOE Chemical Sciences, addresses issues fundamental to the efficient capture and storage of light energy: excited-state formation, chemistry, and photophysics; energy transduction by electron-transfer reactions; and energy storage through chemical transformations. Theoretical and experimental efforts are elucidating the factors controlling excited-state lifetimes and electron-transfer rates; the roles of solvent dynamics, electronic configuration, donor/acceptor separation, bridging groups and nuclear-configuration and free-energy changes are being investigated through studies of transition-metal complexes and other donor/acceptor systems in solution.

Pulse radiolysis and flash photolysis techniques are being used to generate and characterize transient species, including the preparation, properties and reactivity of transition-metal complexes in unusual oxidation states and their ability to bind and activate small molecules, to determine bimolecular and intramolecular electron-transfer rates in solution, and to investigate the radiation chemistry and solvation dynamics of ionic liquids. The properties and reactions of electrons and other ions in dielectric fluids are being studied utilizing both X-ray and high energy electron sources. The Laser-Electron Accelerator Facility (LEAF) enables pulse radiolysis experiments with resolution on the order of 7 picoseconds using electron pulse/laser probe optical spectroscopy. In addition, the 9 MeV electron beam energy at LEAF is ideal for mechanistic studies under novel conditions, such as high pressures or supercritical media.

The long-term storage of solar energy as fuels or valuable chemicals requires efficient coupling of light absorption and chemical transformation processes. Mechanistic studies of systems which couple photo-induced electron-transfer processes to the bond-forming reactions required in the photogeneration of hydrogen and the photoreduction of carbon dioxide to useful chemicals are a major focus. The aqueous chemistry of organometallics is being studied because of their potential in Homogeneous Catalysis in this area.