where Á h i indicates an average over the ensemble of reactive trajectories (see Supplementary Note 4). We show the behavior of N R ðtÞ ¼ M À NðtÞ for several detunings in Fig. . In writing Eq. ( ), we have assumed that every electron transfer event is accompanied by a much faster thermalization of the products (largely into the global ground state in the products side) that allows us to ignore back-reactions. This assumption is well justified if we consider that, for systems with parameters close to our model molecule, the vibrational absorption linewidth is of the order of 0:01_ω P , which represents a timescale suitably shorter than the reaction times estimated from the rate constant, k R!P ¼ 9:4 10 À6 ω P , calculated with the same parameters. In Fig. , we can see that, for Δ ! 0, at early times the reactions proceed in the same way as in the bare case. However, after some molecules have been gathered in the product, the coupling is strong enough for the LP channel to open and dominate over the D ones. This effect is cumulative and the reaction endures a steady catalytic boost. Importantly, the maximum enhancement is observed for resonant conditions where the light-matter coupling is the most intense. On the other hand, with a slightly negative detuning, Δ ¼ À0:02ω P , the reaction is intensified in the early stages (as explained above) but is taken over by the dark states after a relatively short amount of time. Although this off-resonant effect might look appealing, it occurs at an early stage of the reaction when VSC is not technically operative, namely when the energetic separation between dark and polaritonic modes might be blurred by dissipative processes. These considerations are beyond the scope of the current article and will be systematically explored in future work. In conclusion, even though some off-resonant effects might be present at the rate coefficient level, the condition of resonance is essential to observe a significant cumulative acceleration of the reaction (i.e., change in reactant lifetime) with respect to the bare case. Importantly, in the case where the high-frequency mode of the reactant molecules also couples to light, the system is under VSC before the reaction begins and the spectrum in the first excited manifold in the products remains invariant throughout the reaction. Therefore, the rate coefficient is a true rate constant evaluated at N ¼ M, i.e., at the maximum coupling. We will present a detailed analysis of this problem elsewhere.