Hannover 2013 – scientific programme

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MO: Fachverband Molekülphysik

MO 3: SYED: Electronic 2D Spectroscopy from Small to Large Systems I

MO 3.3: Invited Talk

Monday, March 18, 2013, 12:00–12:30, E 415

Resonant 2D Raman Spectroscopy — •Tiago Buckup, Jan Philip Kraack, and Marcus Motzkus — Physikalisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg, D-69120 Heidelberg, Germany

The coupling between structural degrees-of-freedom plays a major role in the evolution of photo-activated chemical reactions. In general, Franck-Condon active modes are not necessarily reactive modes, but can excite reactive modes via intramolecular vibrational coupling. Such a coupling originates from strong anharmonicity terms, which are normally hidden from lower order spectroscopic techniques. Nevertheless, this issue can be addressed by using higher order time domain experiments, like fifth- and seventh-order spectroscopic methods. In this work, we present a resonant fifth-order time-resolved approach to probe the coupling between Raman active modes in electronic excited states. It is based on two consecutive pairs of resonant excitations (k₁/k₂, k₃/k₄) followed by a resonant probe interaction (k₅). The first two pairs of excitations (k₁/k₂) and (k₃/k₄) are resonant with different electronic transitions, inducing vibrational coherences from Raman transitions in, e.g., the excited electronic state. Since the resonant signal is orders of magnitude stronger than non-resonant contributions, cascaded χ⁽³⁾-contributions are strongly suppressed. Our method is applied to a series of structurally different samples (dyes, carotenoids, etc.) in condensed phase. The results show that vibrational coupling can survive e.g. relaxation dynamics that involve conical intersections.