The dynamics of interstitial H2 and its isotopes in crystalline Si were studied by using a potential-energy function, for the molecule, that consisted of the superposition of potentials for 2 separated H atoms as generated by quantum-mechanical calculations. The rotational properties were calculated by using the approach of Martin and Fowler, and the vibrational properties of the molecules as a whole were obtained. The results of the calculations indicated a nearly free rotational motion which was consistent with shallow rotational potentials. Confinement of the molecules led to center-of-mass vibrations of a few hundred wave-numbers and a so-called dynamical off-centeredness that broke tetrahedral symmetry and permitted purely vibrational transitions to occur. This approach has also been used to investigate tetrahedral interstitial H2 adjacent to a bond-centered O atom. The results of these calculations provided a framework for understanding the ro-vibrational properties of H2 and O-H2 and their isotopes; including experiments involving uniaxial stress.

Dynamics of Interstitial H2 in Crystalline Silicon. W.B.Fowler, P.Walters, M.Stavola: Physical Review B, 2002, 66[7], 075216 (6pp)