Shaul Mukamel, of the University of California, Irvine is supported by an award from the Chemical Theory, Models and Computational Methods program in the Division of Chemistry. Mukamel and his coworkers design cutting-edge spectroscopy experiments and develop models and methods for interpreting the results. Understanding and controlling the motions of electrons and nuclei in molecules can determine the rates and outcomes of chemical reactions and energy transfer processes. These include the conversion of solar energy into electric energy in natural photosynthesis and in artificial light harvesting devices. This program develops methods for studying these elementary events by measuring the response of complex molecules to sequences of ultrafast optical laser pulses. Such experiments are made possible by newly-developed laser sources. Models and practical computational tools are developed for the interpretation and analysis of these experiments and extracting the underlying molecular information. Professor Mukamel and his research group collaborate closely with leading experimental research groups all over the world.
Novel experimental techniques involving carefully-timed pulse sequences are designed and broadly applied to molecules and molecular aggregates as well as in the condensed phase. Spectroscopic techniques that aim at the direct detection of electronic and vibrational coherence, as well as nonadiabatic dynamics where the Born Oppenheimer approximation breaks down, are developed. Broadband resonant and off-resonant Raman techniques that can directly probe the passage of molecules through conical intersections are designed, and adequate protocols for their simulation are developed. A highly-intuitive, diagrammatic superoperator formalism is developed for computing the response of molecules to quantum and stochastic light and applied towards creating novel optical pulse sequences by utilizing pulse shaping, phase control, and chiral polarization configurations. New nonlinear signals aimed at providing unambiguous spectroscopic signatures of conical intersections through electronic and nuclear coherences are investigated. The quantum properties of light, such as photon entanglement are used as additional tools for probing molecules and chromophore aggregates by providing information that is not accessible by classical light. For example, entangled and squeezed photons offer temporal and spectral resolutions not achievable by other means. Detection schemes that combine coincidence measurements of individual entangled photons and interferometry are explored and used to investigate the elementary charge and energy migration processes in light harvesting in photosynthetic antennae and reaction centers. Signals involving multiple photon coincidence with temporal and spectral gating are predicted. Photon statistics measurements and higher-order radiation field correlation functions are calculated and shown to provide novel spectroscopic tools for molecular dynamical processes. Incoherent detection schemes of coherent optical signals by fluorescence or electric currents, which are very sensitive and can allow the study of single molecules are developed and investigated.
