REFRACTIVE-INDEX AND DENSITY VARIATIONS IN LIQUIDS - PROGRESS IN THEORETICAL FORMULATION

New progress in the theoretical formulation of the density fluctuation of the refractive index (dn(2)/dd)(p) or DFRI have been performed by two improvements in our previous derivation. The approximation of the polarizability isotropy has been applied at the end of differentiations and the spherical shape together with a packing factor have been considered in the calculation of the molecular cavity volume. As in the previous study the number N of molecules per volume unit, the temperature T and the pressure P are the independent variables. In the final expression, the isothermal term (partial derivative n(2)/partial derivative d)(p,T) related to light scattering intensity is identical but the smaller mixed one is modified. Three hundred and five liquids have been tested and the results, compared to the experimental values deduced form (dn/dT)(p) and (dd/dT)(p) measurements, show a strong improvement in the forecasting of DFRI values.