Vibrational response functions for multidimensional electronic spectroscopy in non-adiabatic models

TL;DR

This paper derives analytical response functions for multidimensional electronic spectroscopy in non-adiabatic models, capturing nuclear-electronic interplay and providing insights into various physical processes in molecular systems.

Contribution

It introduces a novel analytical framework for response functions in non-adiabatic systems, including derivations up to sixth order and validation against numerical calculations.

Findings

Analytical expressions for response functions are derived for complex non-adiabatic models.

The series convergence is demonstrated through comparison with numerical results.

The approach applies to processes like ground state bleaching and stimulated emission.

Abstract

The interplay of nuclear and electronic dynamics characterizes the multi-dimensional electronic spectra of various molecular and solid-state systems. Theoretically, the observable effect of such interplay can be accounted for by response functions. Here, we report analytical expressions for the response functions corresponding to a class of model systems. These are characterized by the coupling between the diabatic electronic states and the vibrational degrees of freedom resulting in linear displacements of the corresponding harmonic oscillators, and by nonadiabatic couplings between pairs of diabatic states. In order to derive the linear response functions, we first perform the Dyson expansion of the relevant propagators with respect to the nonadiabatic component of the Hamiltonian, then derive and expand with respect to the displacements the propagators at given interaction times, and finally provide analytical expressions for the time integrals that lead to the different contributions to the linear response function. The approach is then applied to the derivation of third-order response functions describing different physical processes: ground state bleaching, stimulated emission, excited state absorption and double quantum coherence. Comparisons between the results obtained up to sixth order in the Dyson expansion and independent numerical calculation of the response functions provide an evidence of the series convergence in a few representative cases.