Cavity-Enabled Enhancement of Ultrafast Intramolecular Vibrational Redistribution over Pseudorotation

We studied a single-step ultrafast energy exchange process of Fe(CO)5 under vibrational strong coupling (VSC), with the aim of elucidating the influence of VSC on chemical reactions. Fe(CO)5 has two competing channels to exchange energy between vibrational modes: pseudorotation and intramolecular vibrational energy redistribution (IVR). Ultrafast infrared spectroscopy shows that under VSC, when polaritons are excited, the overall vibrational energy exchange dynamics are accelerated, with IVR becoming faster than pseudorotation. In contrast, the vibrational dynamics initiated in the dark modes under VSC remain unchanged. This work demonstrates that initialization through polariton and reservoir states can afford different dynamics and suggests that the basic concept of VSC-modified chemistry – polaritons can influence reactions – holds, regardless of current controversies over the thermally-activated VSC-modified reactions.