DETERMINATION OF MOLECULAR ORIENTATIONAL ANGLES IN THE LOW-TEMPERATURE PHASE OF C-60

The low-temperature structure of C-60 is simple cubic, however, orient ational long-range order is far from being complete. According to curr ent understanding C-60 molecules can adopt two orientational states ob tained by rotations about [1 1 1] axes through angles close to 98 degr ees and 38 degrees. We present results of an elastic diffuse neutron-s cattering investigation being clearly incompatible with these values a nd yielding rotational angles close to 102 degrees and 42 degrees inst ead, The significance of this finding is the following : While the pre vious angles can be interpreted as an attempt to reconcile icosahedral molecular symmetry with long-range cubic lattice symmetry the new ang les can be understood as the result of an optimized arrangement of nea rest-neighbor molecules, The molecular orientational states, therefore , are indicative of the dominant role of short-range interactions in t his system.