HIGH RESOLUTION INFRARED SPECTRA OF SMALL CRYSTALS OF BARIUM AND THALLOUS AZIDE.
Loading...
Date
1969
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Ohio State University
Abstract
The vibrational spectra of large sized crystals of sodium, potassium and cesium azides have been studied by $Bryant.^{1}$ In the present study, high resolution spectra in the region $4000-200 cm^{-1}$ of single crystals of anhydrous barium azide (dimensions $5.00\times 1.00\times 0.10 mm$) and thallous azide (dimensions $2.50\times 0.70\times 0.014 mm$) have been recorded using a dual Perkin Elmer $6\times$ microsampling attachment with a Perkin Elmer 621 grating spectrophotometer. A large number of bands were observed for barium azide. The selection rules for the internal and lattice vibrations and their combinations were calculated by the ``unit cell'' $method^{2}$ in terms of the crystal structure proposed by $Choi^{3}$ from the neutron diffraction data. Due to low space group symmetry and the presence of two distinct azide ions, multiple splitting of the fundamental modes were observed. Four closely spaced strong bands in the symmetric stretching region (approx. $1360 cm^{-1}$) have been assigned to the infra-red forbidden $\nu_{1}$ frequency, which is allowed by breakdown of selection rules due to asymmetry in one of the azide ions. The spectrum shows good agreement with the neutron diffraction results and the crystal structure described by the space group $C^{2}_{2h}-P2_{1}/m$. The greater sensitivity of barium azide to shock and heat compared with the alkali metal azides can be correlated with the presence of asymmetry in the lattice. The spectrum of thallous azide is similar to that of potassium and cesium azide and supports the accepted space group $D^{18}_{4h}-I4/mcm$. An interesting feature is the fact that the asymmetric stretching frequency $(\nu_{3})$ is at a lower energy compared with the alkali metal azides. This would suggest that the azide ions are more labile in thallous azide.
Description
$^{1}$ J. Bryant, J. Chem. Phys. 45, 689 (1966) and references therein. $^{2}$ S. Bhagavantam and T. Venkatarayudu, ``Theory of Groups and Its Applications to Physical Problems'' (Andhra University Press, Waltair, India, 1951) p. 127-140. $^{3}$ Chang S. Choi, to be published (1969).
Author Institution: Solid State Branch, Explosive Laboratory, Feltman Research Laboratories
Author Institution: Solid State Branch, Explosive Laboratory, Feltman Research Laboratories