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Higher fullerenes – Thermodynamic stability – Endohedral helium chemical shifts
Abstract:
For all isolated pentagon isomers of the fullerenes C60–C86 with nonzero HOMO–LUMO gap and for one nonclassical C72 isomer (C2 v), endohedral chemical shifts have been computed at the GIAO-SCF/3-21G level using B3LYP/6-31G* optimized structures. The experimental 3He NMR signals are reproduced reasonably well in cases where assignments are unambiguous (e.g. C60, C70 and C76). On the basis of the calculated thermodynamic stability order and the comparison between the computed and experimental 3He chemical shifts, the assignments of the observed 3He NMR spectra are discussed for all higher fullerenes, and new assignments are proposed for one C82 and one C86 isomer (C82:3 and C86:17). The calculated helium chemical shifts also suggest the reassignment of the δ(3He) resonances of two C78 isomers.
