Endo -E ‡ Exo , as a function of the lightmatter coupling strength A 0 for both of the critical angles shown in Fig. . At small values of light-matter coupling (A 0 < 0.05 a.u.), negligible selectivity is predicted. Our calculations predict that, at these critical angles, prominent endo selectivity can be achieved at or above A 0 = 0.10 a.u. at which the TS barrier energy difference is greater than 2 k B T at room temperature. For the exo isomer, the selectivity is weaker and requires at least A 0 = 0.20 a.u. for the same degree of selectivity induced by the TS barrier energy difference. Hence, in the experiment, strong selectivity in thie reaction is already achievable with current plasmonic cavity designs. Furthermore, while possible, it is often difficult to control the orientation of the molecules with respect to the cavity's electric field polarization (ϕ, θ). In experiment, we expect random orientation of the molecules during the reaction, so we calculate the angular average of some observable O(ϕ, θ) as,