Research note refractive index in a dilute solution of molecules with intramolecular coupling up to third order in the external field

The effect of the intramolecular coupling on the refractive index, up to third order in the external field amplitude, is studied for a dilute aqueous solution in which the solute molecules are described by a simple model consisting of two coupled harmonic electronic potentials displaced in both equilibrium distance and energy. The effect of the intramolecular coupling on the refractive index appears to be sizeable, particularly in the weak- and intermediate-coupling region.