Coupling photoisomerization reactions to an optical cavity have also been shown to alter the reactive outcomes, both experimentally 3 and theoretically. Fig. (i), adapted from Ref. 13, presents the model isomerization reaction, with a ground state PES (black curve) which has two welldefined minima that correspond to the cis and trans configurations. The excited state |e⟩ (cyan curve) is modeled with a relative flat PES due to the delocalization of the electron density. Panels (ii)-(iii) present the modifications of the polariton potentials due to lightmatter coupling, for two different cavity photon frequencies. In the zero coupling case, outside the cavity (i), the nuclear wavepacket, once excited to the state |e⟩, can freely explore the excited PES. Once the decay channels take over (radiative and non-radiative decay), the system will relax back to the ground state |g⟩, and end up in either in the cis or the trans nuclear configuration. The reaction exhibits barely any selectivity for the cis or trans configuration. When the molecules are coupled inside the cavity (ii-iii), the excited surface curvatures are modified specifically based on the cavity frequency. For cavity frequency ω c = 2.18 a.u. (ii), the emerging feature of the potential is a new barrier on the upper polariton surface. Through a Franck-Condon excitation of the system, a nuclear wavepacket is placed on the upper polariton surface. Due to the presence of the new barrier, the nuclear wavepacket is trapped on the left side (cis) which gives cis selectivity upon relaxation to the ground state. Alternatively, for cavity frequency ω c = 3.13 a.u. (iii), a nuclear wavepacket starting on the lower polariton surface transfers to the trans side of the nuclear configuration space and becomes trapped in a potential well, resulting in trans selectivity upon relaxation to the ground state. As a consequence, the percent yield of the isomerization reaction (iv) can be controlled to be nearly 100% cis or 100% trans by tuning the cavity frequency.