Extended infrared studies of high pressure hydrogen.

Abstract

We have studied solid molecular hydrogen down to liquid helium temperatures and to a pressure of 191 GPa in a new spectroscopic system, extending the low frequency limit by more than a factor of 3, from 3000 to 1000 ${\mathrm{cm}}^{\ensuremath{-}1}$. No evidence for the earlier reported Drude behavior is found within our range of study; a possible explanation of this earlier report is presented. We find a new lattice mode which may be important for determining the structure of the high pressure A phase. Observation of an IR active vibron in the A phase of parahydrogen sets restrictions on the phase diagram.