We study the dissociation dynamics of a diatomic molecule, modeled as a Morse oscillator, coupled to an optical cavity. Surprisingly, we find that the reaction rate decreases for cavity frequencies significantly below the fundamental transition frequency of the molecule. This suppression in the reaction rate occurs when certain key nonlinear resonances in the classical phase space of the molecule disappear, possible only when the dipole function is nonlinear. Future studies should address what happens for multiple molecules in a cavity and molecules with more than one intramolecular vibrational degree of freedom, as well as understand why experiments observe modified reaction rates at the fundamental transition frequency.
Recent experiments of chemical reactions in optical cavities have shown great promise to alter and steer chemical reactions, but the origin of resonant effects between the cavity and certain vibrational modes in the collective limit is still poorly understood. Here, we study unimolecular dissociation reactions of many molecules collectively interacting with an infrared cavity mode through their vibrational dipole moment. We find that the reaction rate can slow down when the molecules are aligned but is unaffected when they are randomly aligned.