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

More information

Identifiers

ORCID for Benno Meier: orcid.org/0000-0003-2258-1507

ORCID for Richard Whitby: orcid.org/0000-0002-9891-5502

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

Catalogue record

Export record

Altmetrics