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 solventdielectric constant ε s , 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 ε s . The Rayleigh ratio R anis describing the anisotropic contribution to light scattering is found to contain a factor [(ε s +2)/3]4 (in addition to another correction) in contrast to the usually assumed [(ε s +2)/3]2 factor. The experimental ratio of the ratio R anis (solution)/R anis (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.