Insights into the mechanisms of optical cavity-modified ground-state chemical reactions

In this work, we systematically investigate the mechanisms underlying the photon frequency-dependent rate modification of ground-state chemical reactions in an optical cavity, as well as the effects of the collective coupling of two molecules to the same cavity photon mode. Our analysis is grounded in a symmetric double-well description of the molecular potential energy surface. To obtain reaction dynamics, we employ a numerically exact open quantum system approach, namely, the hierarchical equations of motion in twin space with a matrix product state solver. Our results reveal that the reaction rate can be modified when the cavity frequency closely matches the transition energy between a pair of vibrational eigenstates. This modification arises due to the opening of a cavity-induced intra-molecular cotunneling pathway, and the extent of rate modification is determined jointly by several kinetic factors. For an anharmonic molecular system with multiple vibrational transition energies, we predict the possibility of observing multiple peaks in the photon frequency-dependent rate profile. Increasing the light-matter coupling strength not only enhances the intensity and the width of the peaks in the rate profile but may also lead to the fusion of two nearby peaks. Furthermore, we find that when two identical molecules are simultaneously coupled to the same resonant cavity mode, an intermolecular reaction channel is activated, contributing to a further alternation in the reaction rate. It is worth emphasizing that, the rate modification due to these intramolecular and intermolecular cavity-promoted reaction pathways remains unaffected regardless of whether the molecular transition dipoles are aligned in the same or opposite direction as the light polarization. This suggests that the cavity-induced rate modification can persist in an isotropically disordered system, differing inherently from the influence of direct intermolecular dipolar interaction, which shows an opposite rate modification tendency in these two dipole orientations.