NMR shielding in helium-3 atoms modified by gaseous nitrogen and oxygen

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.