PROTON SPIN RELAXATION BY PARAMAGNETIC MOLECULAR OXYGEN

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Abstract
The proton spin–lattice relaxation time, T1, was measured for oxygen solutions of water, methanol, and acetone at different temperatures and resonance frequencies of 10.8, 20.0, and 29.8 Mc/s. The contribution of O2 to the relaxation was assumed to be due to the dipole–dipole and hyperfine interaction between the proton spins and the unpaired spins of the O2 molecule. The correlation times of the two interactions were related to the motion and the size of the polymeric cluster of the solvent. Activation energies for the two correlation times were obtained for the oxygen–water system from the dependence of the relaxation time on the resonance frequency. No separation of the two terms was possible for either the oxygen–methanol or oxygen–acetone systems because of their independence of magnetic field variations. The correlation time of the hyperfine term was postulated to be a measure of the extent of solvent–oxygen hydrogen bond strength in all the measured systems.

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