Vibrational wave packet induced oscillations in two-dimensional electronic spectra. I. Experiments

TL;DR

This paper demonstrates how vibrational wave packets influence two-dimensional electronic spectra, revealing oscillations linked to electron-phonon interactions in a dye molecule through advanced ultrafast spectroscopy techniques.

Contribution

It introduces experimental methods to observe vibrational wave packet effects in 2D spectra and connects spectral modulations to molecular dynamics via the frequency correlation function.

Findings

Oscillations in 2D spectra are caused by vibrational wave packets.

Spectral modulations relate to the frequency correlation function.

Experimental techniques reveal electron-phonon coupling effects.

Abstract

This is the first in a series of two papers investigating the effect of electron-phonon coupling in two-dimensional Fourier transformed electronic spectroscopy. We present a series of one- and two-dimensional nonlinear spectroscopic techniques for studying a dye molecule in solution. Ultrafast laser pulse excitation of an electronic transition coupled to vibrational modes induces a propagating vibrational wave packet that manifests itself in oscillating signal intensities and line-shapes. For the two-dimensional electronic spectra we can attribute the observed modulations to periodic enhancement and decrement of the relative amplitudes of rephasing and non-rephasing contributions to the total response. Different metrics of the two-dimensional signals are shown to relate to the frequency-frequency correlation function which provides the connection between experimentally accessible observations and the underlying microscopic molecular dynamics. A detailed theory of the time-dependent two-dimensional spectral line-shapes is presented in the accompanying paper [T. Mancal et al., arXiv:1003.xxxx].