Knowledge Bank

The long wavelength normal mode vibrations of tetragonal potassium azide crystal have been analyzed using two-body analytical interaction potentials and the rigid molecule approximation. The $N3-$, molecules are treated as rigid dynamical units capable of translations and librations. The electrostatic interactions considered include Coulomb, dipole, quadrupole and octopole contributions and it is shown that the multipole interactions have the largest effect on R($A2g$) mode where the azide molecules have equal and opposite librations. The calculated normal mode frequencies are compared with the experimental observations available.