The Vibrational Spectra of Molecules and Complex Ions in Crystals IV. Ammonium Bromide and Deutero-Ammonium Bromide

Abstract

The infra‐red spectra of thin non‐scattering films of NH₄Br and ND₄Br were obtained at 28°C, −78°C and −190°C. The spectra of both compounds in Phase III are in agreement with the x‐ray symmetry, D_4h⁷. The torsional oscillation frequencies occur at 319 cm⁻¹ and 230 cm⁻¹ in NH₄Br and ND₄Br, respectively. The spectra of Phase II are similar to those of the chloride and indicate a structure in which the NH₄⁺ ions are disordered in their equilibrium orientations. There is no evidence of free rotation at any temperature studied. The spectra support x‐ray evidence for a further transition at −100°C in ND₄Br to Phase IV which has symmetry T_d¹ as in NH₄Cl.