Direct measurement and calculation of the second refractivity virial coefficients of gases

Abstract

Values of second refractivity virial coefficients B _R, obtained by differential measurement of the optical path in a gas when a sample is decompressed, are reported for Ne, Ar, Kr, Xe; CH₄, CH₃F, CH₂F₂, CHF₃, CF₄; CO₂, N₂ and SF₆, at four wavelengths 632·8, 514·5, 488·0 and 457·9 nm. There is evidence of a possible wavelength dependence of B _R. First refractivity virial coefficients A _R are also reported for helium and the above gases at the same four wavelengths.

The classical statistical-mechanical theory of B _R is briefly reviewed and extended, and the leading contributions to B _R have been evaluated numerically by computer for eleven of the twelve gases. Agreement between theory and experiment is often within the large experimental limits, but there is a tendency for the calculated values to exceed the observed.