IMPLICATIONS OF THE HIGH-PRESSURE CRITICAL-POINT OF HYDROGEN ON THE STRUCTURE OF THE H-A PHASE

It has been speculated that the recently observed H-A phase in hydroge n is the metallic molecular phase, but there is both experimental and theoretical uncertainty. Theoretical results are sensitive to the crys tal structure. In this paper, based on a symmetry argument, we show th at the structure is probably hcp with the molecular distribution havin g cylindrical symmetry about the crystal c-axis.