Optical properties of a guest molecule in a discrete lattice

Abstract

The optical properties of a simple model system consisting of an anisotropic guest molecule situated on a lattice site of a cubic lattice, the other sites being occupied by isotropic solvent molecules, are found. The results are compared to those found by a continuum (Onsager) approximation. It is found that some quantities, such as the dependence of the energy shift on the solvent dielectric constant εs, are qualitatively little affected by the discrete lattice structure, while others, such as radiative lifetimes and scattering cross sections, have a qualitatively different behavior for large εs. The Rayleigh ratio Ranis describing the anisotropic contribution to light scattering is found to contain a factor [(εs+2)/3]4 (in addition to another correction) in contrast to the usually assumed [(εs+2)/3]2 factor. The experimental ratio of the ratio Ranis (solution)/Ranis (gas) for CS2 and benzene in cyclohexane is satisfactorily reproduced by the present treatment while the continuum approximation gives a result about 20% too high. Some special optical properties arising from the anomalous dispersion of the energy bands of a simple cubic lattice are discussed.