The effect of anisotropic intermolecular interactions on the pressure response of polymeric fullerenes

High pressure Raman scattering was used to probe the pressure response of the two-dimensional tetragonal and rhombohedral C₆₀ polymers. The phonon frequencies as a function of pressure for the various Raman modes of the polymeric phases show a slope change near ∼4 GPa. As pressure increases above 4 Gpa, the pressure coefficients for the majority of the modes exhibit reversible change to lower values. These changes may be attributed to a possible structural modification of the polymers from their initial state, which is characterized by highly anisotropic intermolecular interactions (strong in-plane covalent bonds and weak out-of-plane van der Waals interactions), to a more isotropic one upon application of the external pressure. This behavior is a common theme of other fullerene materials displaying bonding anisotropy.