Second virial coefficients of unsymmetrical and polar fluids

The second virial coefficients of twenty-one polar and/or non-symmetrical molecules have been fitted to these equations: (i) B(T) = b0 – a1T (exp (a2/T) – 1); (ii) B(T) = b0 – a1T–1/2 exp (a2/T); (iii) B(T) = –b0 [a1T (exp (a2/T – exp (ε/kT) + aT (exp (ε/kT – 1) – 1]. The first two equations have a semi-theoretical basis in the quasi-chemical or association approach. The first equation is a temperature modified square-well potential while the third equation is a two-step temperature modified square-well potential. [Continues.]