Colloquium FRIAS Research Focus Quantum Transport - Shaul Mukamel: Probing Charge and Energy Transfer in Molecules by Multidimensional Stimulated Raman Spectroscopy with optical and X ray pulses
von 13:15 bis 14:00
|Wo||FRIAS, Albertstr. 19, Seminarraum|
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universitätsoffen / open to university members
Electronic and vibrational coherences can be impulsively created and manipulated in molecules by ultrashort optical pulses. We demonstrate how a stimulated Raman detection of an optical probe may be used to monitor the phase-sensitive dynamics of nonequilibrium electronic and nuclear wavepackets. Three detection modes are compared - frequency dispersed transmission, integrated photon number change, and total pulse energy change. These various signals offer different windows into the molecular response described by correlation functions of electronic polarizabilities. Linear signals are compared with the more complex quadratic Raman detection involving hybrid short and long probe pulses. We further discuss the interplay of spectral and temporal resolution using the stochastic Liouville equations.
Ultrafast nonlinear x-ray spectroscopy is made possible by newly developed free electron laser sources. We propose how to use stimulated X-ray Raman spectroscopy (SXRS) with broadband attosecond X-ray pulses to probe energy and charge transfer dynamics in biomolecules. In this technique, one X-ray pulse creates localized valence excited state wavepacket around the target atom through a Raman process and its evolution is then probed by another X-ray pulse after some time delay. We study long-range charge transfer in azurin and in cytochrome P450. Simulations show that the ultrafast duration of X-ray pulses and the atomic selectivity of core X-ray excitations offer high spatial and temporal resolution. SXRS offers a complementary observation window to UV and IR techniques.
Many important photophysical and photochemical molecular processes take place via conical intersections (COIS). So far the experimental evidence for their existence is only circumstantial. Femtosecond stimulated Raman spectroscopy (FSRS) signals of conical intersections in the excited state dynamics of the acrolein molecule made using an ab initio surface hopping simulation protocol are presented.
A new technique TRUE-CARS, Transient Redistribution of Ultrafast Electronic Coherences in Attosecond Raman Signals, that can detect the passage through a COIS is presented. An off-resonant composite attosecond and femtosecond probe pulse directly detects electronic coherences that appear as the system approaches the CI.
 “Monitoring Long-Range Electron Transfer Pathways in Proteins by Stimulated Attosecond Broadband X-ray Raman Spectroscopy”, Y. Zhang, J. D. Biggs, N. Govind and S. Mukamel, J. Phys. Chem. Lett. 5, 3656 (2014).
 "Characterizing the Compound I and II Intermediates in the Cytochrome P450 Catalytic Cycle with Nonlinear X-ray Spectroscopy: A Simulation Study", Yu Zhang, Jason D. Biggs, and Shaul Mukamel. Chem Phys Chem (In Press, 2015)
 " Monitoring conical intersections in the ring opening of furan by Attosecond Stimulated X-ray Raman Spectroscopy",Weijie Hua , Sven Oesterling , Jason Biggs , Yu Zhang , Hideo Ando , Regina De Vivie-Riedle , Benjamin Fingerhut. Nature Comm. (submitted, 2014)