Ortho-para conversion of isolated interstitial H2 in single-crystalline Si was studied by Raman scattering. This process was suggested to be caused by the interaction of H2 with the nuclear magnetic moment of 29Si. At 77K, the ortho-to-para conversion rate was approximately 0.015/h for all Si samples employed in the experiments. At 300K, the reverse para-to-ortho transition was observed. It occurred with a rate of roughly 0.18/h and results in a thermodynamically non-equilibrium ortho-para ratio.

Ortho-Para Conversion of Interstitial H2 in Si. M.Hiller, E.V.Lavrov, J.Weber: Physical Review Letters, 2007, 98[5], 055504