Rotational excitations in solid hydrogen and deuterium in the ordered state

New rotational Raman spectra have been obtained in solid ortho-hydrogen and para-deuterium. In the orientationally ordered state a total of five librational lines was observed in the region 5 → 30 cm–1 which is consistent with a previous proposal that the generally accepted Pa3 structure be replaced by a rhombohedral distortion of Pa3, namely, text-decoration:overlineR3. However, the J= 0 → 2 spectra of para-hydrogen and ortho-deuterium impurities have four lines, three of which seem to fit the Pa3 structure. We conclude that a consistent picture of the ordered state has to include additional interactions such as a libron-phonon coupling.