Vibronic Coupling. IV. Trimers and Trigonal Molecules

The mathematical treatment of vibronic coupling in trimers and in benzene is presented. The vibronic matrix is diagonalized by computer methods for weak, intermediate, and strong coupling limits. Perturbation solutions in the two cases, ε≫1≫λ2 and ε≪1≪λ2 are presented. The first case is shown to be analogous to the Jahn—Teller case. Calculated spectra and vibronic probability densities are presented. The values of ε and λ for the real systems, barrelene, triquinacene, and benzene are estimated, and the systems are classified as strong, weak, and intermediate coupling, respectively. This method gives qualitative agreement with the observed benzene spectrum.