Low Temperature Infrared and Raman Spectra of the Ammonium Halides

Using infrared and laser Raman techniques the vibrational spectra of seven of the eight low temperature phases of the ammonium and deuteroammonium halides (halide $\mathrm{ion}={\mathrm{Cl}}^{-}$ , Br⁻, and I⁻) have been recorded. More complete assignments than previously available have been made for the vibrations of crystalline ${\mathrm{NH}}_4^{+}$ and ${\mathrm{ND}}_4^{+}$ ions of T_d and D_2d symmetries. These include assignments for longitudinal components of infrared active vibrations. Frequencies of acoustical translations are inferred by assigning combinations involving the ν₁(A₁) ammonium ion lattice vibrations and acoustical translations.