title: Nuclear magnetic resonance of hydrogen molecules trapped inside C70 fullerene cages.
abstract: We present a solid-state NMR study of H2 molecules confined inside the cavity of C70 fullerene cages over a wide range of temperatures (300 K to 4 K). The proton NMR spectra are consistent with a model in which the dipole-dipole coupling between the ortho-H2 protons is averaged over the rotational/translational states of the confined quantum rotor, with an additional chemical shift anisotropy δ(H)(CSA)=10.1 ppm induced by the carbon cage. The magnitude of the chemical shift anisotropy is consistent with DFT estimates of the chemical shielding tensor field within the cage. The experimental NMR data indicate that the ground state of endohedral ortho-H2 in C70 is doubly degenerate and polarized transverse to the principal axis of the cage. The NMR spectra indicate significant magnetic alignment of the C70 long axes along the magnetic field, at temperatures below ~10 K.
authors.affiliation: School of Chemistry, Southampton University, Southampton SO17 1BJ (United Kingdom). s.mamone@soton.ac.uk.
authors.forename: Salvatore
authors.initials: S
authors.lastname: Mamone
authors.forename: Maria
authors.initials: M
authors.lastname: Concistrè
authors.forename: Ivo
authors.initials: I
authors.lastname: Heinmaa
authors.forename: Marina
authors.initials: M
authors.lastname: Carravetta
authors.forename: Ilya
authors.initials: I
authors.lastname: Kuprov
authors.forename: Gary
authors.initials: G
authors.lastname: Wall
authors.forename: Mark
authors.initials: M
authors.lastname: Denning
authors.forename: Xuegong
authors.initials: X
authors.lastname: Lei
authors.forename: Judy Y-C
authors.initials: JY
authors.lastname: Chen
authors.forename: Yongjun
authors.initials: Y
authors.lastname: Li
authors.forename: Yasujiro
authors.initials: Y
authors.lastname: Murata
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Turro
authors.forename: Malcolm H
authors.initials: MH
authors.lastname: Levitt
keywords: C70; cryogenic nmr spectroscopy; endofullerenes; quantum dynamics; solid-state nmr spectroscopy