Distorted allotropes of bi-benzene: vibronic interactions and electronic excitations

Bi-benzene - chemically bound two benzene molecules in stuck position is studied both analytically and numerically. There are several allotropes of bi-benzene having different geometry. The reason of the existence of sundry distorted structures is the pseudo-Jahn-Teller effect. The parameters of vibronic couplings causing distortions are found. For the calculation of these parameters both, the vibronic coupling of carbon atoms in different C ₆ rings and the vibronic coupling in the rings are considered. The contribution of the distortion of C ₆-planes to the latter coupling is also found. The energies of all the electronic states of π -electrons in all bi-benzene allotropes are determined by using the calculated vibronic interaction parameters. (paper)