It was recalled that the absence of an ortho-para splitting of the H2 line, and an apparent low-symmetry found in stress experiments, had led to the misconception that interstitial H2 had an associated barrier that prevented rotation. The discovery of a new vibrational line for interstitial HD, and its interpretation, had established that interstitial H2 was a nearly free rotator. The consequent insights had led to simple explanations for the microscopic properties of interstitial H2 and an O-H2 complex. The results of Raman studies had led to the suggestion that ortho- and para-H2 had differing diffusivities. However, new results on the formation of complexes of interstitial O with para-D2 and ortho-D2 suggested that the para and ortho species had similar diffusivities at room temperature.

Interstitial H2 in Si - Are All Problems Solved? M.Stavola, E.E.Chen, W.B.Fowler, G.A.Shi: Physica B, 2003, 340-342, 58-66