Raman spectra and the dynamic structure of the high pressure phase of NH4Br (V) and ND4Br (V)

Similar Raman spectra are observed at high pressures for phases II and V of ND₄Br and NH₄Br. Deuteration lowers the II–V phase transition from 20 to 9 kbar at 296 K. ND₄Br V and NH₄Br V are interpreted as mixed phases, and their spectra as the superposition of the spectra of two other phases, III (antiparallel arrangement of the NH₄⁺ ions) and IV (parallel arrangement). The phonons which become Raman inactive at the V–IV phase transition are assigned to clusters or domains of phase V which have antiparallel arrangement.