The isotope effect on the Raman spectrum of molecular C60

High-resolution Raman spectra of solutions of C60 in CS2 reveal the presence of 13C isotopes in the C60 molecules. The observed frequency shifts for the high-energy Ag(2) totally symmetric mode can be explained in terms of first-order non-degenerate perturbation theory. Information on the frequencies of modes close to Ag(2) is obtained by studying the conditions under which a non-degenerate perturbation expansion is valid. This is done with the help of non-perturbative calculations based on first-principles and empirical vibrational models.