Evaporation studies of higher fullerenes and fluorine derivatives of C60

The Knudsen Cell Mass Spectrometry Method has been applied to evaporation studies of fullerenes. The saturated vapour pressures and the sublimation enthalpies of higher fullerenes C-76 and C-84, and a fluorine derivative, C60F18, were determined as thermodynamic characteristics of the pure compounds. Partial characteristics of the higher fullerene mixture were also established for the higher fullerenes. The considerable difference observed between the sublimation enthalpy for the pure compound and the partial mole value, indicates that the higher fullerene mixture cannot be regarded as an ideal solution. In general, an increase in the size of fullerene molecule leads to increase in its sublimation enthalpy. The reverse tendency was observed for fluorofullerenes, in that the more fluorine atoms that are attached to the cage, the greater the volatility. This is evidently associated with different intermolecular interactions in the solid phase, which are weaker when the fullerene molecule is surrounded by an outer sphere of fluorine atoms.