Relaxation Processes in Water. The Spin–Lattice Relaxation of the Deuteron in D2O and Oxygen-17 in H217O

Abstract

An experimental study of the deuteron relaxation time T1 has been made over a temperature range − 18–178°C. The equation for the temperature dependence of the relaxation time is of the form − lnT1 = ln(aeb/T + ced/T). The data are interpreted in terms of an equilibrium leading to a species which relaxes by an isotropic rotational diffusion process. Using transition rate theory and a quadrupole coupling constant derived for the relaxing species from dielectric data, heats and entropies are calculated for both the equilibrium and rate processes. For the equilibrium ΔH = 6.8 ± 0.2 kcal mole−1 and ΔS = 24.8 ± 0.9 e.u. mole−1. For the rate, ΔH* = 2.50 ± 0.06 kcal mole−1 and ΔS* = 3.6 ± 0.1 e.u. mole−1. Similar measurements for the oxygen-17 relaxation time T1 over the temperature interval − 14–180°C yield for the equilibrium ΔH = 5.6 ± 0.3 kcal mole−1 and ΔS = 20.7 ± 1.4 e.u. mole−1. For the rate, ΔH* = 2.43 ± 0.08 kcal mole−1 and ΔS* = 3.9 ± 0.2 e.u. mole−1. The results are discussed in terms of models for the water structure, the species present in the liquid, the relaxation process and molecular motion in the liquid.