Ortho-para conversion of interstitial H2 in Si.

Ortho-para conversion of isolated interstitial H2 in single-crystalline Si is studied by Raman scattering. This process is suggested to be caused by the interaction of H2 with the nuclear magnetic moment of 29Si. At 77 K the ortho-to-para conversion rate is approximately 0.015 h(-1) for all Si samples employed in the experiments. At 300 K, the reverse para-to-ortho transition is observed. It occurs with a rate of roughly 0.18 h(-1) and results in a thermodynamically nonequilibrium ortho-para ratio.