As demonstrated by the theoretical works above, these cavity-induced CIs can play a major role in the dynamics of photochemical reactions. The features of enhanced non-adiabatic coupling and Berry phase offer new mechanisms for an optical cavity to control photochemical reactivity. With that said, more experimental work is needed to demonstrate clear evidence of these cavity-induced CI features and to verify the proposed theoretical mechanisms of how cavity-induced CIs can control photochemical reactivity. All of the above examples are considering a single molecule coupled to the cavity, whereas the possible collective effect 223 of using PICIs for chemical reactivity will be discussed in Sec. 6.3.