THE THERMODYNAMICS OF C-60 FULLERITE AS A SYSTEM OF CLOSE-PACKED SPHERICALLY SYMMETRICAL MOLECULES WITH SHORT-RANGE INTERACTION

The crystalline structure of solid fullerite C-60 and the behavior of intermolecular interaction in this material leads one to classify it w ith materials of close-packed spherically symmetric molecules with sho rt-range interaction. The thermodynamic characteristics of the materia ls in this class obey the laws of similarity, according to which all o f those parameters are dimensionless functions of quantities made up b y the well depth in the intermolecular interaction potential, D, and t he equilibrium intermolecular distance R(o). The foregoing law of simi larity is used to treat the known data on the temperature dependence o f the pressure of saturated vapor above the fullerite surface, which h elped refine the value of D = 0.257 eV, which was previously known wit h considerable scatter. This value is used in checking the validity of the laws of similarity for the thermodynamic parameters of fullerite known from experiment. The validity of the laws of similarity enables one to derive estimates of the critical parameters, the melting and bo iling points of fullerene, and the modulus of elasticity, as well as t he Debye temperature. The resultant data are analyzed from the standpo int of revealing the possibility of existence of fullerene in the liqu id state.