Electronic Structure of the Azide Ion and Metal Azides

Section B reviews the electronic structure of the isolated azide ion. Theoretical calculations of its electronic energy levels and of the distribution of charge about the ion form the basis for understanding the manner in which the azide ion interacts with its environment. The methods and results of the calculations are reviewed first, followed by a discussion of experiments in which the electronic structure is exhibited. The results of X-ray photoelectron spectroscopy are discussed in detail, since this technique effectively maps the electronic structure from the deep (core level) states up (in energy) to the valence levels. 

A simple theoretical formalism for understanding electronic structure is presented in Section C. The gross features of the structure in a particular metal 

Section D discusses the electronic and transport properties of the materials from (primarily) an experimental point of view. The experimental techniques involved are briefly reviewed, forming a basis for assessing the various experimental results. Selection between conflicting interpretations and critical evaluations of certain results and interpretations are performed where this is possible. 

The azide ion has not been observed in nature as an isolated species. It is, however, readily stabilized by a lattice or solution environment. Many of the ion s properties tend to be similar to those of halogen ions when it is ionically bonded or in solution. Indeed, X-ray structural data on NaNa and KN3 reveal that the ion is a compact prolate spheroid (see Chapter 3) comparable in volume to Br its electron affinity (see below) is also close to that of Br . 

Optical absorption spectra of the alkali azides and of the ion in solution display common features (see below), suggesting that the ion s internal electronic transitions are not strongly perturbed by its environment. Further, the azide ion s internal vibrational modes do not differ appreciably from one ionic metal azide to another (see Chapter 4). This can be taken as further evidence that the ion s internal covalent bonding, and hence electronic structure, is relatively insensitive to its surroundings. Thus an understanding of the azide ion s electronic structure is a prerequisite to that of metal azide compounds. 

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