Vibrational study ofenriched13C60crystals

The infrared (IR) spectrum of solid ${\mathrm{C}}_{60}$ exhibits many weak vibrational modes. Symmetry breaking due to ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$ isotopes provides a possible route for optically activating IR-silent vibrational modes. Experimental spectra and a semiempirical theory on natural abundance and ${}_{}{}^{13}{}_{}{}^{}\mathrm{enriched}$ single crystals of ${\mathrm{C}}_{60}$ 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.