An Internuclear J-Coupling of 3He Induced by Molecular Confinement

The solution-state C-13 NMR spectrum of the endofullerene He-3@C-60 displays a doublet structure due to a J-coupling of magnitude 77.5 +/- 0.2 mHz at 340 K between the He-3 nucleus and a C-13 nucleus of the enclosing carbon surface. The J-coupling increases in magnitude with increasing temperature. Quantum chemistry calculations successfully predict the approximate magnitude of the coupling. This observation shows that the mutual proximity of molecular or atomic species is sufficient to induce a finite scalar nuclear spin-spin coupling, providing that translational motion is restricted by confinement. The phenomenon may have applications to the study of surface interactions and to mechanically bound species.