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The nature of the simplest transport processes in water, namely, self-diffusion and shear viscosity, is analyzed on the basis of a version of the microinhomogeneous structure model. The study predicts the existence of locally ordered groups of molecules, taking into account considerations of acoustic properties, light scattering, and computer simulation findings. In particular, it is shown that the anomalous properties of water in supercooled states are mainly connected with the existence of quasiordered regions, which we call clusters. Furthermore, the spatial sizes and evolution times of the crystal-like clusters, as well as the temperature dependence of their fraction volume, are established. Special invariants of the characteristic parameters of molecular motion are pointed out. Finally, it is shown that the self-diffusion in supercooled water is caused by the processes of formation and destruction of crystal-like clusters, while the processes of internal partial reconstruction give the main contribution to the shear viscosity coefficient.

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The main attention of this article is focused on the study of the physical mechanisms of thermal motion in water and water + electrolyte solutions that lead to the broadening of the incoherent neutron scattering peak. It is taken into account that the neutron peak has a diffusion nature and is described by a Lorentzian line shape only for wave vectors k having magnitudes |k| ≡ k , 1/a, where a is the interparticle spacing. A modified version of the theory developed by Singwi and Sjolander (Phys. ReV. 1960, 119, 863) for the description of the Lorentzian half-width is proposed. It is shown that for k > 1/a, the neutron peak is described by a Gaussian line shape whose half-width is proportional to the average thermal velocity of the Lagrange particles. The relevant theoretical parameters can be determined by fitting experimental data for the half-width of the neutron peak. In such a way, the self-diffusion coefficients of water molecules, their collective parts, and the residence times as well as the radii of the Lagrange particles for the pure water and water + electrolyte solutions were determined. It is established that the specificity of the self-diffusion process in water + electrolyte solutions is mainly determined by the relation between a and the radius r I + of the cations I + . The hydrated shell becomes more stable as the inequality r I + < a/2 becomes stronger. In the opposite case, its stability decreases. It is shown that the sizes of the Lagrange particles determined by different independent methods are consistent with each other. This fact is very important, since it testifies to the self-consistency of the obtained results. † Part of the "Josef M. G. Barthel Festschrift".