Mean polarizabilities and second and third virial coefficients of the gases C2H4, C2H6, and SF6

Mean polarizabilities ₀(₀, T) as well as second and third virial coefficients B(T) and C(T) of the equation of state of the gases C₂H₄, C₂H₆, and SF₆ have been determined from refractive index measurements with a Michelson interferometer for wavelength ₀=632.99 nm in the overall ranges 250 KT 340 K and 0p3 MPa of temperature T and pressure p. Some negative C(T) values at low temperatures have been obtained. The C(T) data could be fitted satisfactorily to the simple three-parameter function C(T)= a(T–T₀) exp[ –b(T–T₀)], with the maximum near the critical temperature T_c. A possible correlation between C(T) and the vapor pressure p_v(T) is discussed.