Electron-spectroscopy study ofLiC60:Charge transfer and dimer formation

$\mathrm{Li}-{\mathrm{C}}_{60}$ compounds ${\mathrm{Li}}_{\overline{x}}{\mathrm{C}}_{60}$ were studied for average Li concentration $\overline{x}<~1$ using photoelectron spectroscopy. Strong evidence is found for the formation of ${\mathrm{LiC}}_{60}$ dimers, as well as a second phase. The study suggests that the smallest alkali-metal Li bonds to ${\mathrm{C}}_{60}$ largely ionically for certain configurations. An investigation of the Li $1s$ level shows that under certain conditions the energetics favor a backdonation of the transferred electron to the Li ion.