title: Electrical detection of ortho-para conversion in fullerene-encapsulated water.
abstract: Water exists in two spin isomers, ortho and para, that have different nuclear spin states. In bulk water, rapid proton exchange and hindered molecular rotation obscure the direct observation of two spin isomers. The supramolecular endofullerene H2O@C60 provides freely rotating, isolated water molecules even at cryogenic temperatures. Here we show that the bulk dielectric constant of this substance depends on the ortho/para ratio, and changes slowly in time after a sudden temperature jump, due to nuclear spin conversion. The attribution of the effect to ortho-para conversion is validated by comparison with nuclear magnetic resonance and quantum theory. The change in dielectric constant is consistent with an electric dipole moment of 0.51±0.05 Debye for an encapsulated water molecule, indicating the partial shielding of the water dipole by the encapsulating cage. The dependence of bulk dielectric constant on nuclear spin isomer composition appears to be a previously unreported physical phenomenon.
authors: School of Chemistry, University of Southampton, Southampton SO17 1BJ, UK.
authors: Benno
authors: http://orcid.org/0000-0003-2258-1507
authors: B
authors: Meier
authors: School of Chemistry, University of Southampton, Southampton SO17 1BJ, UK.
authors: Salvatore
authors: S
authors: Mamone
authors: School of Chemistry, University of Southampton, Southampton SO17 1BJ, UK.
authors: Maria
authors: M
authors: Concistrè
authors: School of Chemistry, University of Southampton, Southampton SO17 1BJ, UK.
authors: Javier
authors: J
authors: Alonso-Valdesueiro
authors: School of Chemistry, University of Southampton, Southampton SO17 1BJ, UK.
authors: Andrea
authors: A
authors: Krachmalnicoff
authors: School of Chemistry, University of Southampton, Southampton SO17 1BJ, UK.
authors: Richard J
authors: RJ
authors: Whitby
authors: School of Chemistry, University of Southampton, Southampton SO17 1BJ, UK.
authors: Malcolm H
authors: http://orcid.org/0000-0001-9878-1180
authors: MH
authors: Levitt