Simulating two-dimensional correlation spectroscopies with third-order infrared and fifth-order infrared--Raman processes of liquid water

TL;DR

This paper develops a rigorous computational approach to simulate complex 2D infrared and IR-Raman spectra of liquid water, revealing detailed mode interactions and anharmonic couplings under realistic thermal conditions.

Contribution

It introduces a nonperturbative, non-Markovian simulation method for 2D spectroscopies of water using hierarchical equations of motion in mixed Liouville-Wigner space.

Findings

Spectra exhibit positive and negative peaks indicating mode interactions.

Thermal relaxation and dephasing effects are incorporated.

Simulations reveal detailed intermolecular and intramolecular couplings.

Abstract

To investigate the possibility of measuring the intermolecular and intramolecular anharmonic coupling of balk water, we calculate third-order two-dimensional (2D) infrared (IR) spectra and fifth-order 2D IR-IR-Raman-Raman spectra expressed in terms of four-body correlation functions of optical observables. For this purpose, a multimode Brownian oscillator model of four interacting anharmonic oscillators strongly coupled to their respective heat baths is employed. The nonlinearity of the system-bath interactions is considered to describe thermal relaxation and vibrational dephasing. The linear and nonlinear spectra are then computed in a non-Markovian and nonperturbative regime in a rigorous manner using the discretized hierarchical equations of motion in mixed Liouville-Wigner space (DHEOM-MLWS). The calculated 2D spectra for stretching-bending, bending-librational, stretching-librational, and stretching-translational modes consist of various positive and negative peaks exhibiting essential details of the intermolecular and intramolecular mode-mode interactions under thermal relaxation and dephasing at finite temperature.