The 3618.4 and 2642.6/cm infrared absorption lines of interstitial H2 and D2 in Si were studied under applied uniaxial stresses. The resultant splittings and their small dependence upon isotope-type established that H2 in Si was a nearly free rotor and that these lines arose from vibrational transitions between ro-vibrational states with rotational quantum number J = 1 (T2 in Td symmetry) for ortho-H2 and para-D2.

Rotation of Molecular Hydrogen in Si - Unambiguous Identification of Ortho-H2 and Para-D2. E.E.Chen, M.Stavola, W.B.Fowler, J.A.Zhou: Physical Review Letters, 2002, 88[24], 245503 (4pp)