Multi-state vibronic dynamics of the benzene cation: Combined multi-mode Jahn-Teller and Pseudo Jahn-Teller Effects

The multi-state vibronic interactions in the benzene radical cation are investigated theoretically, based on an ab initio quantum dynamical approach. The three lowest doubly degenerate and two lowest non-degenerate electronic states are included, amounting to eight electronic component states and 28 vibrational degrees of freedom. The multi-mode dynamical Jahn-Teller as well as pseudo Jahn-Teller effects are included on an equal footing. This becomes possible by employing the Multiconfigurational Time-Dependent Hartree Method and its multi-layer extension for the wavepacket propagation underlying the dynamical treatment. The results indicate a step wise population transfer from higher to lower-energy electronic states. The transfer between the highest ( E ∼ and D ∼ states) is extremely fast which is made plausible by their energetic proximity. On the other hand the transfer is not complete and does not comprise the X ∼ ground state. Rather, a substantial part of the population gets trapped in the lowest excited ( B ∼ ) state. The phenomenon is briefly discussed and calls for future work on this intricate dynamical system.