Fig. 3: Observed and simulated Raman spectra of Th₂@I_h(7)-C₈₀.

The low-energy Raman spectrum of Th₂@C₈₀ with 633 nm excitation is shown in black. Computed spectrum (in red) fits well with the experimental one if all the frequencies are shifted by 15 cm⁻¹ to higher values. The symmetric stretching mode of Th₂ (at 152 cm⁻¹) is active in Raman and is coupled with a cage–Th vibration. The associated normal mode is also represented.