MEGABAR PRESSURE TRIPLE POINT IN SOLID DEUTERIUM

Solid orthodeuterium and mixed ortho-para crystals have been studied b y infrared and Raman spectroscopy to a pressure of 186 GPa. We observe two clear phase transition lines and a triple point where they meet; no critical point is observed as reported for hydrogen. We believe tha t previous reports of a critical point in hydrogen are erroneous. Symm etry arguments are used to identify and narrow down the possible struc tures for the various phases.