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 differentiation s and the spherical shape together with a packing factor have been con sidered in the calculation of the molecular cavity volume. As in the p revious study the number N of molecules per volume unit, the temperatu re T and the pressure P are the independent variables. In the final ex pression, the isothermal term (partial derivative n(2)/partial derivat ive d)(p,T) related to light scattering intensity is identical but the smaller mixed one is modified. Three hundred and five liquids have be en tested and the results, compared to the experimental values deduced form (dn/dT)(p) and (dd/dT)(p) measurements, show a strong improvemen t in the forecasting of DFRI values.