SYNCHROTRON X-RAY STUDY OF ORIENTATIONAL ORDER IN SINGLE-CRYSTAL C-60 AT ROOM-TEMPERATURE

Synchrotron x-ray Bragg intensities from a C60 single crystal were used to evaluate the nonuniform atomic density distribution on a C60 sphere at 300 K. Coefficients of the symmetry-adapted spherical harmonics up to l = 18 are required with a resulting density deficiency of approximately 16% in [111] directions and four lobes of approximately 10% excess about [110]. The results are discussed in terms of an effective potential which a single C60 sees in the cubic field of its neighbors. Initial calculations give a maximum rotational potential barrier height of about 2kT or approximately 600 K.