Phase Study of NH3 to 100GPa by Infrared Absorption

Infrared absorption spectra for solid ammonia were measured with diamond anvil cell at room temperature and pressures up to 120 GPa. Two phase transitions were observed at about 40 and 70 GPa, transition from solid V to VI and to solid VII. Four branch peaks were observed for the NH stretching vibrations. One branch showed a significant frequency decrease from 3200 cm-1 at 10 GPa to 3000 cm-1 at 120 GPa, while the other two branches markedly showed the peak shifts to high frequency. No evidence was obtained for the hydrogen-bond symmetrization.