In this work, we examine vibrational coherence in a molecular monomer, where time evolution of a nuclear wavepacket gives rise to oscillating diagonal- and off-diagonal peaks in two-dimensional electronic spectra. We find that the peaks oscillate out-of-phase, resulting in a cancellation in the corresponding pump-probe spectra. Our results confirm the unique disposition of two-dimensional electronic spectroscopy (2D-ES) for the study of coherences. The oscillation pattern is in excellent agreement with the diagrammatic analysis of the third-order nonlinear response. We show how 2D-ES can be used to distinguish between ground- and excited-state wavepackets. On the basis of our results, we discuss coherences in coupled molecular aggregates involving both electronic and nuclear degrees of freedom. We conclude that a general distinguishing criterion based on the experimental data alone cannot be devised.

§Department of Chemical Physics Slovak Technical University Radlinského 9 81237 Bratislava Slovakia

†Institute of Physics Faculty of Mathematics and Physics Charles University Ke Karlovu 5 Prague 121 16 Czech Republic

‡Faculty of Physics University of Vienna Strudlhofgasse 4 1090 Vienna Austria

∥Faculty of Physics Vienna University of Technology Wiedner Hauptstrasse 8 10 1040 Vienna Austria

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