The role of IR inactive mode in W(CO) polariton relaxation process.

Vibrational polaritons have shown potential in influencing chemical reactions, but the exact mechanism by which they impact vibrational energy redistribution, crucial for rational polariton chemistry design, remains unclear. In this work, we shed light on this aspect by revealing the role of solvent phonon modes in facilitating the energy relaxation process from the polaritons formed of a mode of W(CO) to an IR inactive mode. Ultrafast dynamic measurements indicate that along with the direct relaxation to the dark modes, lower polaritons also transition to an intermediate state, which then subsequently relaxes to the mode. We reason that the intermediate state could correspond to the near-in-energy Raman active mode, which is populated through a phonon scattering process. This proposed mechanism finds support in the observed dependence of the IR-inactive state's population on the factors influencing phonon density of states, e.g., solvents. The significance of the Raman mode's involvement emphasizes the importance of non-IR active modes in modifying chemical reactions and ultrafast molecular dynamics.