Molecular dipole moment drives the dynamics of vibrational polaritons in the strong and ultrastrong coupling regimes

Molecular polaritonics is a growing research topic both theoretically and experimentally. However, the underlying microscopic mechanisms for the modification of chemical reactions observed in experiments has yet to be fully understood. To improve our theoretical understanding, models such as the Holstein-Tavis-Cummings or the multi-level quantum Rabi model have been proposed to describe light-matter interaction between quantized fields and molecular transitions. In the strong coupling regime, effects induced by the light-matter coupling may have implications in the modification of chemical reactions, which demands an analysis beyond the RWA. We study the dynamics of anharmonic vibrational polaritons for polar (e.g. R-CO) and non-polar (e.g. CO₂) molecules at equilibrium. We show that the electric dipole function strongly determines the dynamics of vibrational polaritons, and we describe such dependence in detail. Our results hint to a possible mechanism for cavity catalysis of chemical reactions under vibrational strong coupling and the spectroscopy of vibrational polaritons in liquid phase. In addition, our analysis could serve as a benchmark for future developments in the study of polariton chemistry in high-dimensional nuclear configuration spaces and multi-mode cavities.