Revealing Hidden Vibration Polariton Interactions by 2D IR Spectroscopy

TL;DR

This paper demonstrates the use of 2D IR spectroscopy to explore vibrational-polaritons, revealing hidden interactions and developing a quantum model to understand their non-linear optical properties.

Contribution

It introduces the first 2D IR spectra of vibrational-polaritons and a new quantum-mechanical model accounting for anharmonicities, advancing polariton research.

Findings

2D IR spectra differ significantly from free molecules

Revealed hidden dark states and interactions in polaritons

Highlighted the role of anharmonicities in non-linear signals

Abstract

We report the first experimental two-dimensional infrared (2D IR) spectra of novel molecular photonic excitations - vibrational-polaritons. The application of advanced 2D IR spectroscopy onto novel vibrational-polariton challenges and advances our understanding in both fields. From spectroscopy aspect, 2D IR spectra of polaritons differ drastically from free uncoupled molecules; from vibrational-polariton aspects, 2D IR uniquely resolves hybrid light-matter polariton excitations and unexpected dark states in a state-selective manner and revealed hidden interactions between them. Moreover, 2D IR signals highlight the role of vibrational anharmonicities in generating non-linear signals. To further advance our knowledge on 2D IR of vibrational polaritons, we develop a new quantum-mechanical model incorporating the effects of both nuclear and electrical anharmonicities on vibrational-polaritons and their 2D IR signals. This work reveals polariton physics that is difficult or impossible to probe with traditional linear spectroscopy and lays the foundation for investigating new non-linear optics and chemistry of molecular vibrational-polaritons.