Theoretical study of the saturated vapor pressure and enthalpy of sublimation of C-60 fullerite

The saturated vapor pressure and the enthalpy of sublimation of C-60 has been calculated using a virial expansion for the gas and the correlative method of an unsymmetrized self-consistent field for the crystal, from the equilibrium point with the orientationally ordered phase up to the spinodal point estimated as T-s approximate to 1917 K. The Girifalco intermolecular potential is utilized. The dependence lnP(sat)(1/T) is close to a linear one, while Delta H-sub decreases from 172.9 to 140.5 kJ/mole. The results are in good agreement with experimental data available between 600 and 990 K. Scaling of values obtained earlier for Ar gives an estimate for the triple point of the C-60 fullerene: T(tr)approximate to 1460 K, P(tr)approximate to 740 Torr.