Dynamics in Photoexcited Molecules: From Photophysics to Photochemistry

DIPC Seminars

Peter Saalfrank, Universitaet Potsdam, Germany.
Donostia International Physics Center
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Dynamics in Photoexcited Molecules: From Photophysics to Photochemistry Modern laser technology and ultrafast spectroscopies have pushed the timescales for detecting and manipulating dynamical processes in molecules from the picosecond over femtosecond domains (1 fs = 10-15 s), to the so- called attosecond regime (1 as = 10-18s). This way, real-time dynamics of electrons and nuclei after their photoexcitation became accessible experimentally. On the theory side, powerful (quantum) dynamical tools have been developed to rationalize experiments on photon-driven molecular species. In the present talk, three classes of examples for light-induced processes in molecular systems - two from "photophysics", one from "photochemistry" - will be studied with the help of modern quantum chemistry and molecular quantum dynamics. In a first, "photophysical" example the creation of electron wavepackets in molecules by ultrashort laser pulses and their attosecond dynamics will be followed with the help of time-dependent configuration interaction (TD-CI) methods. Stochastic pulse optimization is suggested as a tool to tailor non- linear responses (high harmonic signals) of small molecules such as H2. Much bigger molecules, e.g., diamondoids will be considered in a second example, where the vibronic finestructure in electronic absorption and emission spectra is determined within a time-dependent correlation function approach. This approach has been suggested several decades ago by Heller and coworkers, and is now an efficient method for spectroscopy in complex molecular systems. Also, nonradiative transitions can be treated in this way. Finally, the step to "photochemistry" is made by considering photoswitching of azobenzene and bis-azobenzene molecules. Here, non-adiabatic molecular dynamics with surface hopping allow for detailed insight into the mechanism of photoinduced trans- to-cis isomerization.