Isotopic shifts of the low-energy excitations of interstitial oxygen in germanium

Abstract The rotational states of O in natural Ge as determined by phonon spectroscopy are found to be shifted in isotopically enriched Ge : O crystals. These shifts are larger than compatible with the line width in natural Ge if only the motion of the quasi-free Ge-O-Ge molecule is considered. Because of the reduced isotope scattering of the phonons in the enriched Ge the position of higher excited states could be determined. This allows to estimate the height of the axial potential barrier by extending to Ge : O the Yamada-Kaneta model for Si : O