Raman scattering study of H2 in Si

Isolated interstitial H-2 and H-2 bound to interstitial oxygen (O-H-2) in single-crystalline Si are studied by Raman scattering. Two Raman signals at 3199(1) and 3193(1) cm(-1) (T -> 0 K) are identified as ro-vibrational transitions of interstitial HD. Three lines at 3727(1), 3733(1), and 3740(1) cm(-1) (T -> 0 K) are assigned to ro-vibrational modes of hydrogen molecules in the O-H-2 complex. By monitoring the trapping kinetics of interstitial H-2 at oxygen it is found that ortho- and para-H-2 have similar diffusivities. The temperature dependence of the ortho-to-para ratio of interstitial H-2 suggests that the previously reported [E. V. Lavrov and J. Weber, Phys. Rev. Lett. 89, 215501 (2002)] absence of the para species in Raman spectra at elevated temperatures is due to thermally activated excitation of the molecule from the J=0 to the J=2 rotational state and phonon broadening of the spectral line associated with J=2.