FORCE-CONSTANT MODEL FOR THE VIBRATIONAL-MODES IN C-70

A force-constant model previously developed for C60 is extended to C70. Using the force constants determined for the C60 molecule, the vibrational frequencies for the C70 Molecule are calculated and are identified with the irreducible representations of the D5h symmetry group, according to which the vibrational modes transform. A comparison of the predictions of this model with the experimentally reported values for the Raman- and infrared-active modes shows good agreement overall. The effect of doping by alkali-metal atoms is taken into account by modifying the force constants in order to produce a good fit to the available data for doped C60. The model is then used to predict the frequencies of the Raman- and infrared-active modes in alkali-metal-doped C70.