An FTIR study was made of the stretching modes of OH- and OD- defects, and 4 sharp absorption lines were identified. All of them were proportional in magnitude to the square of the absorption strength of the isolated defects. Equal or opposite changes in strength were observed after quenching, and this clearly divided them into 2 groups. In the case of OH- these were 2 transitions with a large (about 50/cm) spectral splitting, and 2 transitions with a small (about 0.8/cm) spectral splitting. These 2 groups were explained in terms of oscillations of 2 different pair configurations. The first arose from a pair of inequivalent molecular oscillators, with crossed <100> orientations on next-nearest <200> lattice sites with a strong elastic dipole interaction. The second arose from a pair of equivalent <100>-oriented oscillators on nearest-neighbor <110> sites; coupled by static electric dipole interactions and slightly split, by dynamic coupling, into so-called in-phase and out-of-phase modes.

A.Afanasiev, F.Luty: Solid State Communications, 1996, 98[6], 531-4