O isotope effects and vibration-rotation lines of interstitial oxygen in germanium

The infrared absorption of interstitial O-17 and O-18 has been measured at high resolution in natural germanium in a multireflection geometry. The asymmetric mode of O-18 is observed to be broadened by interaction with the phonon background while that of O-17 is unaffected. Tnt: broadening is confirmed by results on an O-18-enriched sample. All the O and Ge isotope shifts can be fitted or predicted rather accurately by a two-parameter semiempirical model using values determined by Pajot and Clauws in 1988. In the multireflection geometry, new lines of low intensity are also observed and they are ascribed to transitions with change of the rotational state of O-16 between the ground and excited vibrational states. Energies of the two-dimensional O-16 rotator are derived from these measurements, with a Ge isotope effect much smaller than the one deduced from phonon spectroscopy