SPECTROSCOPIC STUDIES OF P-H-2 TO ABOVE 200 GPA

Raman and infrared vibrational spectra of H-2 have been measured to pr essures in excess of 200 cpa and at liquid helium temperatures using n ew high sensitivity techniques. Detailed study of the pressure depende nce of o-p conversion rate reveals an initial increase followed by a d ecrease above I cpa. The conversion rate then increases dramatically w ith pressure, and this continues to above 50 cpa. New sets of vibron, phonon, roton, and libron excitations in converted para samples are do cumented as a function of pressure through phases I, II, and III. The results provide important information on the crystal structures, molec ular orientational state, and vibrational dynamics of the high-pressur e phases.