Theory of Resonance Suppression in Vibrational Polariton Chemistry

Recent experiments have demonstrated that it is possible to modify ground-state chemical reactivities by placing an ensemble of molecules in an optical microcavity through resonant coupling between the cavity and vibrational degrees of freedom (DOF) of the molecules. This new strategy of vibrational strong coupling (VSC), if feasible, will offer a paradigm shift in synthetic chemistry through cavity-enabled bond-selective chemical transformations. This so-called VSC regime operates in the absence of any light source, occurs under the resonance condition when cavity frequency matches the molecular vibrational frequency, and only occurs at the normal incidence when considering in-plane momentum inside a Fabry-Perot cavity. In this work, we provide a potential mechanism that explains all observed phenomena. Using numerically exact quantum dynamics simulations and an analytic rate theory, we have demonstrated the resonant suppression of the rate constant when coupling the cavity mode to a vibrational spectator mode in a model reaction. Both the analytic theory and the simulations can explain previously observed phenomena, including the non-linear change of the rate constant when increasing Rabi splitting, modification of both reactive enthalpy and entropy, and for a reason why with a very low barrier, there is a lack of the cavity modification. The analytic theory can also explain the normal incidence condition, and collective coupling effects when solvents are collectively coupled to both cavity mode and reaction coordinate.