Jahn-Teller and related conical intersections in the benzene radical cation and the monofluoro derivate

The multi-state multi-mode vibronic interactions in the benzene radical cation and its monofluoro derivative have been investigated theoretically, based on high-level electronic structure calculations for the system parameters and a quantum treatment of the nuclear motion. The available experimental data are well reproduced. The interplay of different vibronic coupling mechanisms is pointed out leading to multiple nonadiabatic effects. The comparison between the two species treated reveals the intimate connection between Jahn-Teller conical intersections and their more general counterparts occurring between states of different spatial symmetries.