The second virial coefficient of polar rod-like molecules

New method is proposed to determine thermodynamic functions of systems whose molecules interact via the non-spherical Kihara+electrostatic (ES) pair potentials. The second virial coefficient is studied for hard sphero-cylinders or rod-like Kihara molecules with permanent dipoles or quadrupoles embedded in centers of the molecules. Alternative definition of the hard convex body pair potential allows to factorize the many-fold integrals (in the expansion for the electrostatic forces) into a simple integral over center–center (cc) distance and a shape integral over orientational coordinates only. The latter integral was determined for permanent dipole–dipole, quadrupole–quadrupole and dipole–quadrupole interactions and its dependence on the reduced length was expressed in the form of Padé approximant. For pure polar hard sphero-cylinders and polar Kihara molecules the pseudo-experimental data were determined for a series of the reduced lengths and reduced values of the dipole or quadrupole moments and used to test the proposed method. The method is then successfully used to correlate the experimental second virial coefficient of 1,1,1-trifluoroethane and 1,1,1,2-tetrafluoroethane.