Molecular Radiation and Relaxation Processes

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Shaul Mukamel of the University of California Irvine is supported by an award from the Theoretical and Computational Chemistry program to continue his research program aimed at developing theoretical and computational methods for predicting the response of molecules to various external fields, such as light, electric current and other molecules. New experimental approaches related to multidimensional coherent ultrafast laser spectroscopy and to electric current measurements on molecules in quantum junctions are suggested by this theoretical work. A set of tools for their analysis in real space and real time is being developed in the course of the research: signatures of exciton transport in coherent femtosecond optical spectroscopy of chromophore aggregates are being identified; the statistics of single electron transfer events in junctions and of photons emitted in single molecule spectroscopy are being predicted and will be used to explore quantum generalizations of fluctuation theorems connected with the distribution of work and entropy production of driven systems; fluctuations and response functions of quantum systems in nonequilibrium steady states and undergoing transitions between steady states are being studied; and techniques of quantum electrodynamics are being used to predict photon counting statistics and establish fundamental connections between time and frequency resolved nonlinear response functions. This is providing a microscopic description of the incoming and signal fields and allowing the PI and his students to develop new approximation schemes for optical signals.The dynamics of electrons and nuclei in molecules can be effectively probed by monitoring their response to external perturbations such as optical fields, electrical currents and even the response of the probed molecule to interactions with neighboring molecules. Mukamel's work is providing the theoretical tools needed by experimental scientists for analyzing the data produced by different types of experiments. The work is having a broader impact through its application by scientists around the world as well as through the highly interdisciplinary training received by the students in the group. The results of this research have been widely disseminated through Mukamel's textbook, "Principles of Nonlinear Optical Spectroscopy," which he plans to update and expand in the next period of support. This is expected to further broaden the impact of the funded work.