Raman scattering and infrared absorption of the C84 and Sc2@C84 isomers 23:D2d were studied at room temperature and 95 K. The results are compared to the response of pristine and doped C60. According to the lower symmetry and the higher number of atoms C84 exhibits much more vibrational modes than C60, in particular at wave numbers above 500 cm−1. For lower energies the vibrational structure of C84 resembles a downshifted and split C60 spectrum. After the encapsulation of two scandium atoms the overall vibrational structure and the number of C84 modes was preserved as a result of the similar geometric structure. From the very good correlation of the C84 and Sc2@C84 cage modes metal to fullerene charge transfer induced shifts could be analyzed. The lines were found less shifted compared to the C60 modes in exohedral doped A6C60 (A=K,Rb,Cs). Increased line widths of low energy cage modes were attributed to an additional intramolecular relaxation channel related to the dynamics of the encapsulated scandium ions. A set of nine new lines with almost complementary Raman and infrared intensities was found for Sc2@C84 below 200, at 246 and at 259 cm−1, and attributed to Sc–C84 vibrations. These vibrations were further identified as Sc–C84 stretching and Sc–C84 deformation modes. The Sc–C84 valence force constant of 1.19 N/cm was derived with a linear three-mass oscillator model for Sc2@C84. Both, the charge transfer induced line shifts and the Sc–C84 valence force constant indicate an effective transfer of approximately two electrons per scandium to the carbon cage. This is in agreement with an electronic state (Sc2.2+)2@C844.4− previously proposed on the basis of x-ray powder diffraction, x-ray photoemission spectroscopy (XPS), and quantum chemical calculations. The unexpected high number of Sc–C84 vibrations is attributed to crystal field and factor group splitting.

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