Two-Dimensional Spectroscopy and Fast Electronic Processes
David M. Jonas
Department of Chemistry, University of Colorado-Boulder
Fast electronic motions are important in chemistry, photosynthesis, interfacial electron transfer, and in some proposed "next generation" photovoltaics. Our group developed two-dimensional femtosecond spectroscopy, a new method for measuring fast electronic motions in disordered materials mentioned in the recent DOE report on Basic Research Needs for Solar Energy Utilization. We have used this method to probe the fastest electronic motions in molecules, which proceed through "conical intersections" between electronic potential energy surfaces. At conical intersections, the Born-Oppenheimer approximation breaks down, and the motions of the molecular framework and electrons are closely coupled. The new methods allow us to determine the mechanism for electronic motions, in that it characterizes the vibrations which cause the electron "jump" and stabilize the new electronic configuration. Such conical intersections are also thought to be important in interfacial electron transfer and, possibly, in multiple exciton generation for "next-generation" photovoltaics. I will discuss prospects for probing how electronic motions are coupled to the molecular framework for more deeply bound valence and core electrons with the new source.
