Vibrational wave packet induced oscillations in two-dimensional electronic spectra. II. Theory

TL;DR

This paper develops a theoretical framework to understand vibrational effects on two-dimensional electronic spectra, explaining oscillatory behaviors and amplitude variations in spectra of systems weakly coupled to vibrational modes.

Contribution

It introduces a vibrational modulation theory based on Huang-Rhys factors, enabling analysis of time-dependent 2D spectra and explaining experimental observations.

Findings

Predicts oscillations in spectral components due to vibrational coupling

Provides a method to analyze spectra using solvent interaction line-shapes

Applicable to both low and high energy vibrational modes

Abstract

We present a theory of vibrational modulation of two-dimensional coherent Fourier transformed electronic spectra. Based on an expansion of the system's energy gap correlation function in terms of Huang-Rhys factors, we explain the time-dependent oscillatory behavior of the absorptive and dispersive parts of two-dimensional spectra of a two-level electronic system, weakly coupled to intramolecular vibrational modes. The theory predicts oscillations in the relative amplitudes of the rephasing and non-rephasing parts of the two-dimensional spectra, and enables to analyze time dependent two-dimensional spectra in terms of simple elementary components whose line-shapes are dictated by the interaction of the system with the solvent only. The theory is applicable to both low and high energy (with respect to solvent induced line broadening) vibrations. The results of this paper enable to qualitatively explain experimental observations on low energy vibrations presented in the preceding paper [A. Nemeth et al, arXiv:1003.4174v1] and to predict the time evolution of two-dimensional spectra in ultrafast ultrabroad band experiments on systems with high energy vibrations.