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Abstract

Intramolecular vibrational energy redistribution (IVR) plays a significant role in cavity- modified chemical reaction rates. As such, understanding the fundamental mechanisms by which the cavity modifies the IVR pathways is a fundamental step toward engineering the effect of the confined electromagnetic modes on the outcome of chemical processes. To further explore the influence of the strong light-matter coupling on IVR pathways, we evaluated multiple systems and different initial wavefunctions to highlight relevant activation pathways. Initially, we examined an ensemble of M two-mode molecules with third-order intramolecular anharmonic coupling interacting with an infrared cavity mode, analyzing their quantum dynamics and infrared spectra. For specific Rabi splitting resonances and ensemble sizes, the resulting spectrum revealed a Fermi resonance involving polariton states, driven by light-matter coupling. We classified this new polaritonic subsystem as polaritonic Fermi resonances, further categorizing them as type I and type II based on resonance conditions and involved overtones. On the dynamical side, polaritonic Fermi resonances involving fundamental and overtone states of the polaritonic subsystem facilitate efficient energy transfer pathways between otherwise off-resonant molecular states. These pathways, enabled by intramolecular anharmonic couplings, are collective in nature. Consequently, cavity excitation can efficiently spread towards low-frequency modes, becoming delocalized over several molecules. In another system, we analyzed the 6-modes HONO molecule focusing on the reaction coordinate driving the isomerization process. By varying coupling strengths to the cavity, we observed modifications in intramolecular energy pathways, sometimes enhancing or suppressing the isomerization process. Assuming a temperature of 0.0 K and an initial state with overall energy below the energy barrier, the isomerization process primarily resulted from quantum tunneling between the cis and trans wells.