Properties of Specific Ions

Other elements of glass structures must be included in order to discuss more subtle variations in properties and various spectra. The field strength of both network-forming and network-modifying cations must be included in discussions of trends in properties with glass compositional variations. Since many modern studies include variations in the identity of the anions which link the structure, their field strengths and ionic radii are also important. The atomic radii of mobile cations, anions, and atoms and molecules must be considered in structural models seeking to explain transport properties. 

Perhaps the best approach to this problem lies in the study of inert gas solubility and diffusion in glasses. Inert gas atoms can be used as probes of the interstitial regions of glasses. It is also possible that computer simulations of glass structures will aid in understanding the empty space which we all know must exist in these network structures. In any case, it is certain that a full understanding of the structure of a glass has not been obtained until we can confidently predict such basic properties as the density. 

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The absence of such a model is due, in part, to the problems encountered in determining the structure and physicochemical properties of specific ion pairs and in correlating these properties with reaction-rates. Tliis problem is addressed by the data in Table 1, which establish relationships between the physicochemical properties of the solvent-separated M l pairs and electron-transfer rates. In Scheme 2, these relationships and properties are associated with the key species (stable M" pairs as well as transient precursor and successor complexes) pertinent to assessing the rate and energy (AG°et) of electron transfer from BPH2 to 1. As the crystallographic radii of the cations increase from... 

Individual properties of specific ions and solvents are included in k, mainly via the AG°qj.j, term. The preceding account does not do justice to the sophistication of the ion evaporation theory or its recent experimental tests (Gamero-Castafio 2000), but wiU suffice for present purposes. 

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