Theory of Rayleigh molecular light scattering by isotropic polar fluids revisited

TL;DR

This paper revisits the molecular theory of Rayleigh light scattering in dense isotropic polar fluids, deriving simple analytical equations for various scattering contributions by adapting electrostatic local field concepts.

Contribution

It introduces a revised theoretical framework that accounts for rotational and dipole-induced dipole contributions with simple analytical expressions.

Findings

Derived simple analytical Rayleigh ratios for pure DID and pure rotation cases.

Justified the rotational mean field approximation using a single correlation parameter.

Provided expressions for mixed contributions where DID or rotation dominates.

Abstract

The molecular theory of Rayleigh light scattering in dense isotropic polar fluids is reconsidered by suitably adapting local field concepts of electrostatics to propagating electromagnetic waves, hence accounting for both the rotational and dipole-induced dipole (DID) contributions. Simple analytical equations are derived for the various Rayleigh ratios relevant to lateral light scattering in various situations, namely pure DID, pure rotations and mixed contributions. For pure DID, the derived Rayleigh ratios are entirely analytical and very simple, while for pure rotation, the use of rotational mean field approximation is justified, hence allowing the description of Rayleigh ratios in terms of a single orientational correlation parameter that is straightforwardly determined as a positive root of a quadratic algebraic equation. Simple expressions for the Rayleigh ratios are also derived in two mixed situations where DID dominates rotation and when rotation dominates DID. Relation to previous experimental and theoretical work is discussed.