¹³C Isotopjc Effect on the Raman Spectrum and Structure of C₆₀ Fullerene

Abstract

The Raman spectrum of ¹³C enriched C₆₀ samples is recorded and analyzed in comparison with that of undoped ¹²C₆₀. Comparison with the isotopic effect in diamond and in other infinite solid networks is also made.

A frequency shift depending on the amount of 13Q is observed for the C=C stretching vibration, without any splitting. This effect is unusual and is a proof that the C-C is not localized and its double bond character is not isolated but strongly coupled with other bonds in the cage. If the CC bond was independent as in small or non-spherical molecules such as organic compounds, an isotopic effect Δv ≃ 30 cm⁻¹ for ¹²C=¹³C and Δ ≃ 60 cm⁻¹ for ¹³C = ¹³C could be expected and a splitting could appear in the case of uncompleted ¹³C substitution and variable relative intensities could be observed. It is not the case of ¹³C₆₀.

In isotopic C₆₀, all C = C vibrations in the spherical network are strongly coupled; an average isotopic mass must be considered for the randomly distributed isotopic atoms in the material to interpret the experimental result. CßO has thus more solid than molecule behavior.