N3 Vibrations in Metal Azides

Ni exists in sites of varying molecular and crystallographic symmetry in metal azide lattices as described in Chapter 3. The observed mode splittings can provide important information regarding the crystal field in such lattices, while the mode energies can be empirically correlated with the degree of lattice ionicity. 

The azide ion mode frequencies vary from one azide crystal to another, but no systematic trends can be discerned for a series of azides except as discussed below. Internal mode frequencies for some alkaU metal azides are shown in Table III. It was pointed out [38] that a monotonic decrease in frequency with 

The frequencies of the long-wavelength q 0) internal modes differ through a series of azide crystals because of different interionic distances and forces. Details of the interactions were discussed in Section B.3 for cubic sites. If one of the interactions is dominant, there should be a correlation between the frequency of the respective fundamental modes and the magnitude of the interacting forces for crystals of the same structure. The perturbing potential [fXv)] affects the internal force constant according to the relationship 

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