where the equal sign is satisfied under τ c = Ω -1 R . Fig. presents the τ c -dependence of VSC rate constants under different Rabi splittings Ω R , obtained from the numerically exact HEOM simulations (open circles with thin guiding line) as well as the interpolated expression in Eq. 20 (solid lines). All pairs of curves show a similar turnover behavior along τ c but differ in the peak positions. The dashed vertical lines denote the position where τ c = Ω -1 R at the corresponding Ω R value, which coincides with the peak positions of the turnover curves. As a result, the expression of k int VSC predicts that the maximum enhancement of VSC rate constants is reached when τ c = Ω -1 R , in agreement with the numerically exact simulations.