Proton positions in ice polymorphs

It has since been shown by a variety of physical techniques that in some of the high-pressure forms of ice the protons are ordered and in others disordered, in particular, the low-temperature forms IX and VIII are the ordered forms of ice-IIl and ice-vII respectively. The nature of the far infrared absorption bands indicates that the protons are ordered in ii and ix (sharp bands) but disordered in v (diffuse bands). The dielectric properties of all the following forms of ice have been studied ic ii, iii, v, and vi, vii and viii, and the conclusions as to proton order/disorder are included in Table 15.1. 

Polymorph Density (g/cc) Ordered or disordered protons Analogous silica or silicate structure Reference 

The mobilities of the H and OH ions are respectively 32-5 and 17 8 X 10 cm/sec for an applied field of 1 volt/cm, whereas the values for other ions are of the order of 6 x 10 cm/sec. Calculations show that very little energy is required to remove a proton from one water molecule, to which it is attached as (HsO) , to another, for the states H3O, HjO H2O, H3O have the same energy. If we assume that the H ion acts as a bond between two molecules, then the process shown diagrammatically in Fig. 15.3(a) results in the movement of H from A to B. The analogous mechanism for the effective movement of OH ions through water is illustrated in Fig. 15.3(b). Whereas other ions have to move bodily through the water, the H and OH ions move by what Bernal termed a kind of relay race, small shifts of protons only being necessary. 

In order to account for the high dielectric constant of water it is necessary to suppose that there exist groups of molecules with a pseudocrystalline structure, that is, with sufficient orientation of the O-H-0 bonds to give an appreciable electric moment. The upper limit of size of these clusters has been estimated from studies of the infrared absorption bands in the 1-1-1-3 /ii region as approximately 130 molecules at 0°, 90 at 20°, and 60 at 72°C. In a liquid there is constant rearrangement of the molecules, and it is postulated that a given cluster persists only for a very short time, possibly of the order of 10 to 10 seconds. 

In view of the very extensive literature on the structure of water we give here only a few references to the more recent papers which include many references to earlier work.  

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