NMR shielding in helium-3 atoms modified by gaseous nitrogen and oxygen |
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Authors: | Piotr Garbacz Maria Misiak Karol Jackowski |
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Affiliation: | Laboratory of NMR Spectroscopy, Faculty of Chemistry, University of Warsaw, Warsaw, Poland |
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Abstract: | Helium-3 nuclear magnetic resonance (3He NMR) measurements were carried out for the gaseous mixtures of helium-3 with pure nitrogen and synthetic air as the solvents. It was found that 3He shielding is linearly dependent on solvent density up to approx. 6 mol/L. At higher density of the gaseous solvent, the change of 3He shielding is nonlinear and especially distinct when helium-3 atoms can interact with two O2 molecules. The interaction with paramagnetic oxygen molecules can induce two kinds of 3He shielding changes: (1) due to the isotropic Fermi contact interaction and (2) from the dipolar magnetic interaction between unpaired O2 electrons and 3He nuclear magnetic dipole moment. The two paramagnetic effects in helium-3 shielding cannot be experimentally separated, although for such small molecular objects, they could be presumably modeled by advanced theoretical calculations. |
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Keywords: | gas phase 3He NMR helium-3 magnetic shielding intermolecular interactions with N2 and O2 molecules paramagnetic effects in 3He shielding |
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