OBSERVATION OF HIGHER-ORDER INFRARED MODES IN SOLID C-60 FILMS

In this paper, we present a rich (4 strong F1u first-order and an additional 98 weak lines) ir spectrum for a 4-mum-thick C60 film on KBr in the range 400-4000 cm-1. Most of the weak lines are identified with second-order combination modes. More accurate frequencies of some optically inactive modes in C60 have been obtained by simultaneously analyzing the higher-order ir and Raman spectra. Isotope-induced symmetry lowering in C60 molecules has also been observed and is responsible for activating several fundamental modes which would otherwise be ir inactive.