In this fully quantum mechanical treatment, the chemical kinetics process can be easily understood in terms of solvent-mediated population transfer between vibrational states. The molecular sub-system is initially prepared in the ground vibrational state |ν 0,R , 0⟩ (here 0 denotes no photon in the cavity) on the left well of the potential energy surface (shown in Fig. ). Outside the cavity, the ground vibrational state on the left reactant well |ν 0,R , 0⟩ is thermally excited to the vibrationally excited states such as |ν 1 , 0⟩. Then, following a vibrational relaxation from the vibrationally excited states to the ground vibrational state |ν 0,P , 0⟩ on the right (product) well, the forward reaction occurs. In the weak solvent coupling (energy diffusion-limited) regime, the chemical kinetics is dominated by the thermal excitation process. When coupling to the cavity photon mode, the molecular vibrational excitation is hybridized with the cavity excitation, which is reflected in the absorption spectrum Fig. (that resembles experimental observations in Fig. and Fig. ). The thermal excitation due to cavity loss mediated by the coupling of cavity photon modes to other far-field (outside of cavity) modes leads to the creation of a photon inside the cavity which can be absorbed by the molecular sub-system leading to the vibrational excitation. Therefore, coupling to the cavity provides (in addition to the solventmediated thermal excitation |ν 0 , 0⟩ → |ν 1 , 0⟩ outside cavity) an additional pathway