IDENTIFICATION OF THE POLYMERIZED ORTHORHOMBIC PHASE OF C-60 FULLERENE

It is established by x-ray diffraction and Raman scattering that the p olymerization of C-60 fullerene at 1.5 GPa and 723 K leads to the form ation of an orthorhombic phase that is different from the previously i dentified high-pressure orthorhombic phase. It is determined by a calc ulation of the optimal packing of linear C-60 polymers by the method o f atom-atom potentials that the energetically favorable structure of t he orthorhombic phase belongs to the space group Pnnm and not the prev iously proposed group Immm. The computed value of the rotation angle o f the polymer chains that corresponds to the minimum packing energy wa s equal to 61 degrees. The mechanisms leading to the formation of the polymerized phases are discussed on the basis of the results obtained. (C) 1997 American Institute of Physics.