Vibrational Spectrum and Analysis. Silver Azide Crystals

The vibrational spectrum (infrared, Raman, and far infrared) of silver azide crystals has been measured over the frequency range from 40 to 4000 cm⁻¹. A factor‐group analysis was carried out for the classification and determination of selection rules of the $\text{k\hspace{0.17em}≃\hspace{0.17em}0}$ vibrational modes of the crystals. Individual assignments are made for the modes due to lattice transitions, the multiplicity of fundamentals in the infrared and Raman, and for numerous combinations constituting fine structure in the medium infrared. Observed band structure of single‐crystal spectra are strongly influenced by crystal structure orientation with respect to the incident beam. Numerical checks are provided for the assignment of essentially all combinations and indirect determinations are made of the frequencies of several modes which are neither infrared nor Raman active. Discussion is made of observed absorptions which apparently are not governed by factor group selection rules. The over‐all observed spectrum is in general agreement with the reported crystal structure, ${\mathcal{D}}_{\text{2h}}^{26}$ —Ibam.