Ultraviolet photoelectron spectra (UPS) of ${\mathrm{LaC}}_{82}$ questioning whether the La atom is inside the C cage or not are measued for the first time. The UPS of ${\mathrm{LaC}}_{82}$ is analogous to those ${\mathrm{ofC}}_{82}$ but there is a critical differnce in the region just below the Fermi level. It is on appearance of two new peak components at 0.9 and 1.6 eV with the intensity ratio of 1:2 in the UPS of ${\mathrm{LaC}}_{82}$. Their origin is the transfer of three electrons from La to ${\mathrm{C}}_{82}$ to form the electronic structure of ${\mathrm{La}}^{+3\mathrm{}}$${\mathrm{C}}_{82}^{\mathrm{-}3}$. Present results combined with theoretical calculations on the position of the La atom in the molecule assert an encapsulation of the La atom inside the C cage.

• Received 9 August 1993

DOI:https://doi.org/10.1103/PhysRevLett.71.4261