Intercalation ofO2in solidC60and molecular-rotation hindrance

We present ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ NMR experiments performed on pure ${\mathrm{C}}_{60}$ crystalline powders. High resolution in the solid state on a very pure sample allows us to measure an extremely narrow (1.8-Hz linewidth) resonance at 143.6 ppm characteristic of the rotating molecule. The intercalation of ${\mathrm{O}}_2$ molecules in the fcc structure induces an additional resonance (at 144.3 ppm) whose intensity is directly related to the oxygen content. At room temperature the ${\mathrm{O}}_2$ intercalation is partially reversible. By analysis of the ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ resonance shape of this additional resonance we characterize the hindrance in the ${\mathrm{C}}_{60}$ rotation introduced by the intercalated species.