Dispersion curves for the $\left[00\mathrm{}\zeta \right] \left(\Delta \right)$, $\left[\zeta \zeta 0\right] \left(\Sigma \right)$, $\left[\zeta \zeta \zeta \right] \left(\Lambda \right)$, and $\left[\frac{1}{2}\frac{1}{2}\zeta \right] \mathrm{}\left(T\right)\mathrm{}$ directions in N${\mathrm{D}}_4$Cl were measured at 85 °K by inelastic scattering of slow neutrons using the McMaster triple-axis crystal spectrometer at Chalk River. The single crystals were grown from solution. A torsional (librational) branch, flat within about 2%, with an average frequency of 8.3 × ${10}^{12}$ cps, was found. Results are compared with a modified rigid-ion-model calculation based on Parlinski's formulation. Symmetry points and branches in the dispersion curves are classified according to their symmetry species. The Lyddane-Sachs-Teller relation as generalized by Cochran holds within experimental accuracy.

• Received 23 July 1970

DOI:https://doi.org/10.1103/PhysRevB.3.2733