The structures of three structural isomers of Sc2@C84(I, II, III) have been determined by 13C NMR and have Cs, C2v, and D2d point group symmetry, respectively. By IR measurements, we have determined that the peaks below 110 cm-1 originate from the scandium-cage vibrational modes based on temperature-dependent IR experiments. Line broadenings of the Sc-cage modes below 110 cm-1 are quite different from those of the C84 (empty) cage modes in far-IR spectra. Sc-cage vibrational modes below 300 cm-1 in Raman spectra are also identified. The force constants of the Sc-cage vibrations based on a linear three-mass-oscillator model indicate that the charge state of Sc atoms are close to +2.