INTERMOLECULAR VIBRATIONS IN PURE AND DOPED C-60 - AN INELASTIC NEUTRON-SCATTERING STUDY

We discuss the results of inelastic neutron time-of-flight spectroscopy on powder samples of C60, K3C60 and Rb3C60. A well structured density of states is obtained from the raw data where the details can be attributed to translational acoustic/optic and librational modes. The intermolecular excitation spectra for all three compounds can be well understood within the framework of lattice dynamics of a molecular crystal. We show that a particular sample preparation is necessary to avoid impurity contributions in particular within the gap region between inter- and intramolecular vibrations. There are indications for a weak anomalous temperature dependence of low energy phonons in K3C60 at T(c).