Modified excimer properties under collective strong coupling

The interplay between the local molecular dynamics and the collective polaritonic excitation is a fundamental but challenging aspect of polaritonic chemistry. While light-matter strong coupling has been proven to affect chemical properties, the underlying mechanism is still unclear. We employ a recently developed electronic-structure method for collective strong coupling to study the argon excimer, providing a simple prototype for a more general discussion on excimer properties. The computed potential energy surface exhibits a region where electronic, nuclear, and photonic degrees of freedom are strongly intertwined, and we analyze their coupling. Collective strong coupling produces an abrupt transition in the excited state's vibrational landscape, causing the higher vibrational levels to behave similarly to the ground state vibrations. We thus find that collective strong coupling inhibits the formation of the excimer once the collective coupling exceeds a critical value. We propose this is a general feature of excimers under collective strong coupling that requires experimental investigation and offers an additional facet of polaritonic chemistry.