Phase transition inRbC60: Vibrational and electronic properties

In situ Raman scattering, ultraviolet-photoemission-spectroscopy (UPS), and electron-energy-loss-spectroscopy (EELS) measurements have been performed on crystalline films of ${\mathrm{RbC}}_{60}$ through the fcc-to-orthorhombic structural phase transition. The Raman spectra exhibit large changes in intensity of modes not active for isolated icosahedra, including ungerade vibrations. This is attributed to a substantial increase in interfullerene coupling in the presence of ${\mathrm{C}}_{60}$ merohedral disorder. UPS measurements indicate a finite density of states at the Fermi energy for both phases with small changes in the ${\mathrm{C}}_{60}$ derived states through the transition. Low-energy metalliclike excitations are observed in EELS.