Evidence forsp3carbon atoms in theRbC60dimer phase

High resolution ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ NMR experiments prove the existence of ${\mathrm{sp}}^3$ carbon atoms which are assigned to the dimer bonds in the quenched phase of ${\mathrm{RbC}}_{60}$. The relative intensities of the ${\mathrm{sp}}^3$ lines support a model where the ${\mathrm{C}}_{60}$ monomers are connected via a single bond. Spin-lattice relaxation measurements and ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ spectral changes reveal the transition to the polymer phase above 200 K.