ENDOHEDRAL VIBRATIONS OF NA+ IN C-60

We report the results of a theoretical investigation of the possible vibrations of a single sodium cation trapped inside C60. To begin, all-electron local density functional (LDF) calculations provided the total energy of the C60Na+ species with respect to the displacement of the ion along the internal C3-upsilon and C5-upsilon symmetry axes. Consistent with other calculations, we found the positions of equilibrium displaced from the center; thus, tunneling is possible between positions of equilibrium. To analyze this situation, a pair potential for the interaction between the ion and the individual carbon atoms was fit to the LDF-determined energies. A completely anharmonic variational analysis that accounts for the delocalization via tunneling of the ion inside the sphere was used to determine the fundamental frequencies. Clusters of infrared (dipole) active transitions over a wide range of frequencies were found.