In the work the character of water clusterization in the whole existence domain of its liquid state is discussed: from supercooled states to the critical point. Conclusions about the cluster composition of liquid water are drawn based on the analysis: 1) of the features of dielectric relaxation; 2) character of the temperature dependence of its static dielectric permittivity, and 3) the value and temperature dependence of different contributions to the heat capacity of the system. It is shown that near the water crystallization point tetramers prevail in its structure, with an increase in the temperature trimers start to play the main role, and near the critical point of water dimers become the major associates. At temperatures near the water crystallization point the obtained results well agree with the data on emission and absorption X-ray spectroscopy.

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".

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