Relaxation processes in water: Viscosity, self-diffusion, and spin-lattice relaxation. A kinetic model

Experimental measurements of T1 for oxygen-17 water in n-heptane emissions were made in the supercooled region down to −31°C. The data were fit to the double exponential form of the rate equation with activation energies for the two processes of E1=11.85±0.57 and E2=3.54±0.08 kcal mole−1, respectively. Using transition state rate theory, activation entropies ΔS1*=35.3±2.3 and ΔS2*=4.63±0.25 cal deg−1 · mole−1 were calculated. It is proposed that both the low and high temperature reactions are kinetic processes. It is suggested that the large entropy term for the low temperature reaction indicates that the relaxation process involves the ``cooperative'' dissolution of a small cluster of hydrogen bonded molecules. An examination of the available data for viscosity and diffusion indicates that the high temperature relaxation process is the same as that for the rotational (T1) relaxation. It is suggested that this process involves the breaking of a single hydrogen bond. The question of whether the low temperature processes for viscous flow, diffusion, and rotational relaxation are related is discussed.