Vibrational Study of 13 C-enriched C 60 Crystals

The infrared (IR) spectrum of solid C 60 exhibits many weak vibrational modes. Symmetry breaking due to 13 C isotopes provides a possible route for optically activating IR-silent vibrational modes. Experimental spectra and a semi-empirical theory on natural abundance and 13 C-enriched single crystals of C 60 are presented. By comparing the experimental results with the theoretical results, we exclude this isotopic activation mechanism from the explanation for weakly active fundamentals in the spectra.