Spectroscopic investigations of C60 fullerene and its endohedral derivatives.

Abstract

This study presents spectroscopic investigations of C₆₀ fullerenes and endofullerenes.The experimental techniques are: Nuclear Magnetic Resonance (NMR), Inelastic Neutron Scattering (INS) and far-Infrared (far-IR or THz) spectroscopy. The ¹³C solution NMR spectrum of C₆₀ is found to display two small additional ”side peaks”. They arise because of the secondary NMR isotope shift effect, present for isotopomers of C₆₀ with two adjacent ¹³C nuclei. ¹³C enriched C₆₀ displays a broad peak, without the two side peaks seen for natural abundance, due to increased statistical distribution of ¹³C nuclei in the cage. The spectra of the natural abundance and ¹³C enriched C₆₀ are simulated through a Monte-Carlo type technique, which approximates the NMR spectrum of J coupled ¹³C spin clusters by the second moment. ³He@C₆₀ displays a doublet in the solution ¹³C NMR spectrum. This is caused by a non-bonded J-coupling between ³He nucleus and ¹³C. The notation ⁰J_HeC is adopted, in which the superscript zero symbolises the absence of a covalent bond between ³He and ¹³C. ⁰J_HeC increases in magnitude with increasing temperature; consistent with the ³He nucleus coming closer to ¹³C on average as temperature is increased. The ¹³C solution NMR spectrum of CH₄@C₆₀ displays a significant broadening of the ¹³C (C₆₀) peak; which is consistent with a ⁰J_HC coupling between ¹H from endohedral CH₄ and ¹³C from the confining cage. The noble gas endofullerenes ³He@C₆₀, ⁴He@C₆₀ and Ne@C₆₀ are investigated through INS and THz spectroscopy. The atomic translational quantization is probed using these techniques. Defying the odds, He@C₆₀ is shown to absorb THz light which translationally excites the Helium atom. The translational transitions are interpreted using a 3D spherical oscillator model for the endohedral species. The confining potentials for He@C₆₀ and Ne@C₆₀ are obtained by simulating the experimental results. This provides valuable parameters for the non-covalent interaction between the noble gas and the confining C₆₀ fullerene cage.

More information

Identifiers

ORCID for Malcolm Levitt: orcid.org/0000-0001-9878-1180

Catalogue record

Export record