Catalysis by Dark States in Vibropolaritonic Chemistry

TL;DR

This paper reveals that dark vibrational modes in vibropolaritonic systems, previously overlooked, can facilitate vibrational cooling and catalyze reactions by being delocalized across molecules, leading to significant reaction rate enhancements.

Contribution

It demonstrates that dark modes, often ignored, are delocalized and can enhance vibrational cooling and catalysis, explaining experimental reaction rate changes.

Findings

Dark modes are delocalized across 2-3 molecules.

Dark modes enhance vibrational cooling channels.

Reaction rates can increase by approximately 50% due to dark mode effects.

Abstract

Collective strong coupling between a disordered ensemble of $N$ localized molecular vibrations and a resonant optical cavity mode gives rise to 2 polariton and $N-1\gg2$ dark modes. Thus, experimental changes in thermally-activated reaction kinetics due to polariton formation appear entropically unlikely and remain a puzzle. Here we show that the overlooked dark modes, while parked at the same energy as bare molecular vibrations, are robustly delocalized across $\sim$2-3 molecules, yielding enhanced channels of vibrational cooling, concomitantly catalyzing a chemical reaction. As an illustration, we theoretically show a $\approx$50\% increase in an electron transfer rate due to enhanced product stabilization. The reported effects can arise when the homogeneous linewidths of the dark modes are smaller than their energy spacings.