Rotational spectra for off-center endohedral atoms at C60 fullerene

Rotational spectra for endohedral Li+@C60 and Na+@C60 are calculated at different temperatures. Most of the features in these spectra are related with the degree of anisotropy in the atom–cage interaction. While the low anisotropy for Na+@C60 results in rather simple spectra with the 2B oscillation typical of a diatomic molecule, the more eccentric and anisotropic Li+@C60 produces complex spectra with rotational and librational bands. Some interesting effects are induced by the cage rotation, which has been incorporated through a semiclassical formalism.