From the intensities of powder diffraction lines the positions of the deuterons in N${\mathrm{D}}_4$Cl have been determined at liquid nitrogen and room temperatures. The experimental results confirm at low temperature the space group $T_d^{}{}_{}{}^1$ and the tetrahedral structure of the ammonium ion with an $N-D$ separation 1.03A. At room temperature the $T_d^{}{}_{}{}^1$ space group persists. Neither free rotation nor disordered orientations of the ammonium ions have been observed. Details concerning deuteron vibrations are discussed.

• Received 13 February 1951

DOI:https://doi.org/10.1103/PhysRev.83.88