REMARKABLE HIGH-PRESSURE PHASE LINE OF ORIENTATIONAL ORDER IN SOLID HYDROGEN DEUTERIDE

We have studied solid HD to pressures in excess of 100 GPa and to liqu id helium temperatures. We have found the broken symmetry quantum phas e transition of orientational order by means of Raman scattering. The pressure-temperature phase line has a very unusual reentrant behavior, different from the homonuclear isotopes when measured on the same tim e scale. The phase line is explained in terms of the rapid thermalizat ion of rotational levels with changing temperature.