Mean Polarizabilities and Second Virial Coefficients of the Gases Ar, CH4, C2H6, C3H8 and C(CH3)4

Mean polarizabilities α0(λ0, T) and second virial coefficients B(T) of the gases Ar, CH4, C2H8, C3H8 and C(CH3)4 are determined from refractive indices measured with an interferometer in the ranges 260 K ≤ T ≤ 366 K, 0 ≤ p ≤ 3 bar of temperature T and pressure p (λ0 = 546.266 nm). The following results are discussed: α0 depends linearly on T. For each gas B(T)/Vc respectively B(T)/AR can be fitted best versus (Tc/T)2 by two straight lines, which are different for the ranges Tc < T and Tc > T (Tc = critical temperature, Vc = molar critical volume, AR = 4 πNA α0/3). In the range T > Tc the straight line is common to all gases, whereas in the range T < Tc the straight lines are different for all gases. For all gases a linear correlation between α0 respectively AR and Vc exists.