Relaxation processes in water. A study of the proton spin-lattice relaxation time

Abstract

An experimental study of the proton spin‐lattice relaxation time T₁ has been made for H₂O over the temperature interval from −16 to 145°C. It is found that after correction for spin‐rotational interaction, the experimental T₁ behavior can be represented by the double exponential form of the rate expression used to treat the relaxation for the quadrupolar nuclei ²H and ¹⁷O in water. The oxygen‐17 data are used to calculate the intramolecular contribution to the proton T₁. The activation energies $E_1\text{=9.4± 0.8\hspace{0.17em}}\mathrm{kcal/mole}$ and $E_2\text{=3.6± 0.1\hspace{0.17em}}\mathrm{kcal/mole}$ for the two contributions to the intermolecular relaxation are in sufficiently good agreement with those for the intramolecular relaxation to indicate that the relaxation mechanism is the same in both cases. This mechanism involves two processes. The data indicate the process dominant at high temperature can be described as a rotational diffusion where the amplitude of angular motion increases with increasing temperature.