We have developed an analytic theory 9 to explain the rate constant modification and performed exact quantum dynamics simulations to assess its performance. Our theoretical investigation suggests that the VSC modification originates from the cavity mode promoting vibrational excitation |ν L ⟩ → |ν ′ L ⟩. Not surprisingly, it is critical to have the |ν L ⟩ and |ν ′ L ⟩ state description explicitly in order to have the frequency ω 0 explicitly showing up in the theory, and to correctly describe the observed VSC resonance behavior. All of these hints that so long one can have the quantum state description of these key vibrational states, one should be able to obtain the correct VSC resonance condition, even for MQC approaches.