X-Ray Diffraction in Water: The Nature of Molecular Association

Abstract

The x-ray diffraction intensity-angle distribution for water and its variation for a temperature of 2\ifmmode^\circ\else\textdegree\fi{} to 98\ifmmode^\circ\else\textdegree\fi{} C, are given. Two important periodicities of 3.24 and 2.11A and a third of 1.13A at 21\ifmmode^\circ\else\textdegree\fi{}C are established in satisfactory agreement with Meyer. The first one decreases with increasing temperature and the second increases.It is shown that the conception of molecular complexes explains neither the existence of these periodicities nor their change with temperature. In fact, the description of "association" that involves complexes of two or three or more molecules, should be abandoned in favor of the molecular group conception, (cybotactic condition) emphasized by the author. These groups of molecules containing hundreds and perhaps thousands of molecules in each, have a temporary existence as individuals, have illdefined boundaries, possess an optimum size and an internal regularity determined by the temperature and molecular forces, and expand anisotropically. The experimental facts are in agreement with this view. A detailed description of the molecular arrangement in water from x-ray data is not at present possible yet it simulates the crystal arrangement in ice. A mathematical treatment of the forces within and between the molecules in such groups can probably be studied with much profit only from the quantum viewpoint.