High-pressure Raman study of ammonium halides

Raman spectra of NH4X (X = Cl, Br, I) in the range 2800–3200 cm−1 have been obtained at pressures up to 40 GPa at room temperature. The pressure dependences of the n̈1 and n̈3 modes are discussed in relation to hydrogen bonding effects in the crystals. The Raman spectra of ammonium halides show that the n̈3 mode merges to the v1 mode at pressures above 22.5 GPa in NH4Cl, 33.5 GPa in NH4Br and 35 GPa in NH4I.