INSITU INFRARED TRANSMISSION STUDY OF RB-DOPED AND K-DOPED FULLERENES

We have measured the four IR-active C60 molecular vibrations in MxC60 (M = K, Rb) as a function of doping x. We observe discontinuous changes in the vibrational spectra showing four distinct phases (presumably x = 0,3,4, and 6). The 1427-cm-1 and 576-cm-1 modes show the largest changes shifting downward in frequency in four steps as the doping increases. Several very weak modes are visible in the x = 6 phase and are possibly Raman modes becoming weakly optically active. We present quantitative fits of the data and calculate the electron-phonon coupling of the 1427 cm-1 IR mode.