Molecular H was observed directly in crystalline samples by means of Raman spectroscopy. It was found that, at 77K, samples which were exposed to a H/D plasma exhibited 4 vibrational lines (2842.6, 3446.5, 3925.9, 3934.1/cm). Upon using a pure H plasma, only the 2 highest-frequency lines could be seen. In the case of a pure D plasma, only the lowest frequency was detected. These frequencies were attributed to the rotational-vibrational modes of isolated interstitial D2, HD and H2 molecules, respectively.

J.Vetterhöffer, J.Wagner, J.Weber: Physical Review Letters, 1996, 77[27], 5409-12