Tile fact that HD molecules in the solid vibrate and gyrate around the
ir centers of mass, substantially shifted relative to their geometrica
l centers, entails a specific anisotropic interaction, which is absent
in the homonuclear hydrogens. The physical reason behind the pressure
-driven orientational phase transitions in the homonuclear nominally J
= 0 hydrogens is recognized to be the electrical quadrupolar (EQQ) in
teraction, which becomes progressively stronger with increasing pressu
re. Our estimates show that in HD at relatively moderate pressure of a
bout 10 kbar, the specific non-EQQ forces become predominant. The pres
sure-induced orientational order in HD might have an entirely differen
t nature as compared to the homonuclear hydrogens.