INS study of vibrational spectra of NH 4 I at very high pressures

Vibrational spectra of NH4I have been studied by means of incoherent inelastic neutron scattering at pressures up to 10 GPa using a high-pressure cell of the “toroid” type with tungsten carbide anvils. Librational (L) and transverse optical (TO) mode frequencies as a function of pressure were obtained. The observed behavior of these modes may be explained in terms of their hybridization at pressures P>6 GPa. A change of dynamics of NH4I due to this effect is a possible mechanism for the phase transition which occurs in this system at high pressure.