Raman and Brillouin study on solid HCl under high pressure and low temperature

Pressure-temperature (P - T) phase diagram for solid hydrogen chloride (HCl) was determined over a wide region up to 18 GPa in pressure and down to 20 K in temperature, by means of Raman and Brillouin spectroscopies. The results of the Raman experiments demonstrate that the Phase III is stabte in a wide P - T range and exists above 17 GPa at room temperature, and the intermediate phase between Phases I and LII exists in a wide region. The Brillouin experiments clarify the elastic properties of the solid Phase I. The detailed analyses of the Brillouin data also give a suggestion that the intermediate phase can be separated into two phases, i.e., Phases II and I'.