Jahn-Teller coupling in Rydberg series of benzene

Jahn-Teller coupling effects in doubly degenerate Rydberg series (np _x,y and nd_xz,yz, respectively) converging towards the doubly degenerate X̃²E_1g ion core of benzene are analyzed in a multichannel quantum-defect description. The model includes Jahn-Teller coupling (via the lowest-frequency E_2g mode ν₆) in the ion core and in the Rydberg orbitals, as well as the interaction of degenerate electronic channels. Fast internal-conversion processes in the Rydberg manifold of benzene are included in a phenomenological manner via an absorptive imaginary part of the reactance matrix. The model parameters are determined from the analysis of existing multiphoton absorption spectra of low Rydberg members. Absorption spectra of the complete np _x,y and nd_xz,yz series and near-threshold photoionization cross sections are calculated, including hot-band spectra (one quantum of ν₆ excited in the initial electronic state). The results are of relevance for the assignment of the enigmatic vibronic structure of the 3p ¹A_2u and 3p¹E_2u Rydberg states and for the understanding of autoionization dynamics in benzene.