The properties and behaviour of the nuclear spin isomers (NSI) of the water molecule are of great interest in astrophysics since the ortho:para ratio (OPR) is assumed to provide insight into the formation mechanism and history of comets [1] as well as other celestial bodies [2]. Technological advances are also foreseen for ortho-H2O enriched samples in magnetic resonance applications, by analogy with hyperpolarisation experiments using para-hydrogen. Motivated by these perspectives, methodological bottlenecks need to be overcome: 1-the development of efficient separation protocols, and 2-the improvement in storage strategies for water sample enriched in either of its NSI through a better understanding of their inter-conversion mechanism. We will show how magnetic focussing in a supersonic molecular beam [3] provides a convenient method for preparing water vapour strongly enriched (i.e., &gt;15:1) in the ortho-H2O NSI. We will also show that rare gas matrices can be an efficient condensed phase storage medium for enriched samples [4] whose lifetime remains however, limited by the slow interconversion kinetics of NSI causing sample enrichments to decay over several hours. Closer examination of the NSI inter-conversion kinetics of isolated water molecules, trapped in rare gas matrices, revealed that it increases significantly in the heavy water isotopologues H217O and H218O compared to normal water, and that it increases rapidly above T~10K.[5] The temperature and isotope effects may provide valuable insight into the interconversion mechanism and, in particular, the role of confinement on the intramolecular couplings (i.e., spin-rotation and spin-spin) responsible for the inter-conversion between the ortho and para NSI of the water molecule. Finally, perspectives for the application of ortho-H2O to study chemical dynamics at ice surfaces will be discussed. REFERENCES [1] Crovisier, J., et al., Science 1997, 275, 1904-1907; Mumma, M.J. et al., Science 1986, 232, 1523-1528. [2] Hogerheijde, M.R, et al., Science 2011, 334, 338-340. [3] Kravchuk et al., Science 2011, 331, 319-321. [4] Turgeon, P.-A., et al., Phys.Rev.A 2012, 86, 062710. [5] Turgeon, P.-A., et al, J. Phys. Chem. A 2017, 121, 1571-1576.

Preparation, characterization and storage of water vapours highly enriched in its ortho-H2O nuclear spin isomer

255th National Meeting (2018)

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