Synchrotron x-ray study of orientational order in single crystal C60 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 16% in 111 directions and four lobes of 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 600 K.