Molecular vibrations-induced quantum beats in two-dimensional electronic spectroscopy

TL;DR

This paper investigates how high-frequency molecular vibrations influence quantum beats in two-dimensional electronic spectroscopy, distinguishing vibrational effects from electronic coherences in molecular aggregates.

Contribution

It introduces models with various vibrational modes to analyze their impact on 2D spectra and demonstrates how damping affects spectral features.

Findings

Vibrational modes can produce spectral beats similar to electronic coherences.

Damping strength of vibrational modes can be inferred from spectroscopic signals.

Models show how vibrations map onto 2D spectra.

Abstract

Quantum beats in nonlinear spectroscopy of molecular aggregates are often attributed to electronic phenomena of excitonic systems, while nuclear degrees of freedom are commonly included into models as overdamped oscillations of bath constituents responsible for dephasing. However, molecular systems are coupled to various high-frequency molecular vibrations, which can cause the spectral beats hardly distinguishable from those created by purely electronic coherences. Models containing damped, undamped and overdamped vibrational modes coupled to an electronic molecular transition are discussed in this paper in context of linear absorption and two-dimensional electronic spectroscopy. Analysis of different types of bath models demonstrates how do vibrations map onto two-dimensional spectra and how the damping strength of the coherent vibrational modes can be resolved from spectroscopic signals.