Confinement Effects on the Nuclear Spin Isomer Conversion of H2O

The mechanism for interconversion between the nuclear spin isomers (NSI) of H 2 O remains shrouded in uncertainties. The temperature dependence displayed by NSI interconversion rates for H 2 O isolated in an argon matrix provides evidence that confinement effects are responsible for the dramatic increase in their kinetics with respect to the gas phase, providing new pathways for o-H 2 O↔p-H 2 O conversion in endohedral compounds. This reveals intramolecular aspects of the interconversion mechanism which may improve methodologies for the separation and storage of NSI en route to applications ranging from magnetic resonance spectroscopy and imaging to interpretations of spin temperatures in the interstellar medium.