SCATTERING OF THE VIBRATIONAL FREQUENCIES OF C-13(X)C-12(60-X). - A RAMAN-SPECTROSCOPY AND QUANTUM-CHEMICAL STUDY

Through a joint experimental and theoretical study we assess the effect of random C-13 substitution in the vibrational spectra of (C60-xCx)C-12-C-13 First, Raman data are gathered for a 25% C-13-substituted sample. Then, we randomly generate an ensemble of isotopomers of (C60-xCx)-C-12-C-13, with x= 18, 36. For all these isotopomers we calculate the vibrational frequencies and normal modes and project them onto the space of the normal modes of (C60)-C-12 to yield mode scrambling matrices. The accumulation of the resulting mode scrambling matrices gives the frequency dispersion upon random isotopic substitution. Both experiment and theory find that the dispersion of the lower-frequency vibration is multimodal.