Proton positions in Ice

These considerations lead one to seek for a structure in which the integrity of water molecules as structural units is preserved. Several such structures were proposed by Bernal Fowler (1933) based on the two principles that water molecules are preserved and that they link together so that each proton of one molecule is 

A model of one of the possible disordered structures is shown in fig. 2.3. Because the H-O-H angle in a free water molecule is about 105°, which is quite close to the tetrahedral angle of 109° 28, the protons are often drawn as though located exactly upon the 

0-0 bond lines, as we have done in fig. 2.3. This is not, however, a necessary feature of the model, as we shall see later, though the small displacements involved in other configurations seem to have no practical implications. This statistical model can be simply described in terms of the positions of the oxygen nuclei and a 

Electron diffraction studies of thin films of ordinary ice carried out by Shimaoka (i960) confirm this structure, the O-H distance being 0 96 0 03 A. The peaks corresponding to proton positions were observed to be elongated in directions perpendicular to the 

O-H bond, which implies either that the thermal vibrations are anisotropic (which is certainly true) or that the H-O-H angles deviate slightly from the tetrahedral value, an average of the possible misalignments being seen. We shall return to this later. 

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