The H*
2 defect in crystalline germanium

The local vibrational modes of hydrogen in crystalline germanium are studied by infrared absorption spectroscopy and uniaxial stress measurements. Hydrogen isotopes are introduced by proton or deuteron implantation. A dominant trigonal defect involving a pair of inequivalent hydrogen atoms is identified, with local modes at 765, 1499, 1774 and 1989 cm⁻¹. The structure and the local modes of the H*
2 defect are calculated using ab initio local density functional cluster theory. The structure is consistent with the uniaxial stress experiments. The calculated frequencies are in fair agreement and the isotope shifts in good agreement with those observed.