DESCRIPTION OF POLYATOMIC REAL SUBSTANCES BY TWO-CENTER LENNARD-JONES MODEL FLUIDS.

For O//abstract) CO, CS//2, C//2H//4, Cl//2 and Br//2 orthobaric properties were calculated by perturbation theory on the basis of two-center Lennard-Jones (2CLJ) model molecules. The LJ-parameters sigma and epsilon were determined by fitting the vapour pressure and the bubble density at one temperature about halfway between the triple point and 0. 8 T//c. The elongation L in the model was fixed to give the correct temperature variation of the vapour pressure. The temperature variation of the orthobaric liquid density turned out to be less dependent on L, and could be satisfactorily reproduced. With the parameters determined from the orthobaric properties of the liquid, second virial coefficients were calculated. This was also done for Ar, Kr, Xe, CH//4, N//2, F//2 and C//2H//6 for which the parameters have been determined previously in a similar way. The agreement between the predicted and the experimental second virial coefficients is excellent for C//2H//4 and C//2H//6. For O//2, N//2, CO and F//2 it is still better than for the spherical molecules. The agreement for Cl//2 and CS//2 is less satisfactory.