Molecular Exciton Cluster States and Spectra with Application to Benzene

Abstract

A cluster expansion is introduced for the determination of the optical absorption properties of cluster states in substitutionally disordered molecular crystals. This method is based on the Green's function expansion in terms of the localized cluster states in the energy region of the guest sub-band. The general features of the method are illustrated by calculations for a simple two-dimensional molecular crystal. The physical parameters for the calculation are based on the v 11 benzene vibrational exciton. Both polarized and unpolarized cluster optical absorptions display strong asymmetries, with respect to the isolated guest spectral line. Calculations are performed on the monomer, dimer, trimer, and tetramers (three kinds) of the benzene crystal ac -plane.