Temperature dependence of infrared and Raman modes in polymeric RbC60

Abstract

Temperature dependence of the intra-molecular vibrational modes of C60 in the quasi-1D polymeric RbC60, across the low temperature transition at not, vert, similar50 K, has been probed through infrared (IR) and Raman spectroscopies. With the lowering of temperature, the split IR modes of RbC60 are seen to harden but below 50 K a small but definitive signature of an anomalous softening is observed. In addition, the background IR transmission shows an increase below 50 K with the opening of a well defined gap in the electronic spectrum. The implications of these results, along with those of Raman measurements, are discussed in terms of the interaction of intra-molecular phonons with electrons and spin excitations in the system.