Cavity-Enabled Enhancement of Ultrafast Intramolecular Vibrational Redistribution over Pseudorotation

Vibrational Strong Coupling (VSC) between molecular vibrations and microcavity photons yields a few polaritons (light-matter modes) and many dark modes (with negligible photonic character). Although VSC is reported to alter thermally-activated chemical reactions, its mechanisms remain opaque. To shed light on this problem, we followed ultrafast dynamics of a simple unimolecular vibrational energy exchange in Fe(CO)₅ under VSC, which showed two competing channels: pseudorotation and intramolecular vibrational-energy redistribution (IVR). We found that, under polariton excitation, energy exchange was overall accelerated, with IVR becoming faster and pseudorotation being slowed down. However, dark mode excitation revealed unchanged dynamics compared to outside of cavity, with pseudorotation dominating. Thus, despite controversies of thermally-activated VSC modified chemistry, our work showed VSC can indeed alter chemistry upon non-equilibrium preparation of polaritons.

One-Sentence Summary: Vibrational polariton alters ultrafast molecular dynamics in liquid phase, and dark modes show no influences.