Understanding the Nature of Vibro-Polaritonic States in Water and Heavy Water

TL;DR

This study investigates vibro-polaritonic states in water and heavy water under strong light-matter coupling, mapping their evolution across different concentrations and comparing experimental results with simulations to understand their physical properties.

Contribution

It provides a systematic analysis of vibro-polaritonic states in water and heavy water, including experimental mapping and theoretical modeling of their evolution under varying concentrations.

Findings

Vibro-polaritonic states persist even at 400 cm-1 detuning.

Strong coupling regimes are mapped across different water concentrations.

Simulations with oscillator strength correction align with experimental data.

Abstract

One of the most popular subjects now being researched in molecular science is strong light-matter coupling. The introduction of vibrational strong coupling and the formation vibro-polaritonic states tend to modify chemical reactivity, energy transfer, and many other physical properties of the coupled system. This is achieved without external stimuli and is very sensitive to the vibrational envelope of the molecular transition. Water is an excellent vibrational oscillator, which is being used for similar experiments. However, the inhomogeneously broad OH/OD stretching vibrational band make it complicated to characterize the vibro-polaritonic states spectroscopically. In this paper, we performed vibrational strong coupling and mapped the evolution of vibro-polaritonic branches from low to high concentration of H2O and measured the on-set of strong coupling. The refractive index dispersion is correlated with the cavity tuning experiments. These results are further compared with transfer matrix simulations. Simulated data deviate as noted in the dispersion spectra as the system enters into ultra-strong coupling condition. A simple oscillator strength correction is made to include the self-dipolar interaction. Hopfield coefficients are also calculated, showing that even at 400 cm-1 detuning, the vibro-polaritonic states still possess light and matter components. Here, we systematically varied the concentration of H2O and mapped the weak, intermediate, and strong coupling regimes to understand the role of inhomogeneously broad OH/OD stretching vibrational band. Our finding may help to better understand the role of H2O/D2O strong coupling in the recent polaritonic chemistry experiments.