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 asy mmetric mode of O-18 is observed to be broadened by interaction with the ph onon background while that of O-17 is unaffected. Tnt: broadening is confir med 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 semiempiric al model using values determined by Pajot and Clauws in 1988. In the multir eflection geometry, new lines of low intensity are also observed and they a re ascribed to transitions with change of the rotational state of O-16 betw een the ground and excited vibrational states. Energies of the two-dimensio nal O-16 rotator are derived from these measurements, with a Ge isotope eff ect much smaller than the one deduced from phonon spectroscopy.