FTIR STUDY OF 2 TYPES OF OH- OH- AND OD-/OD- DEFECT PAIRS IN KBR/

In a systematic FTIR study of the stretching mode of OH- (and OD-) def ects in KBr, we have identified four sharp absorption lines, all scali ng in strength with the square of the absorption strength of the isola ted defects. Their equal or opposite changes in strength observed afte r thermal quenching clearly divide them into two groups: two transitio ns with a large (similar to 50 cm(-1)) and two with a small (similar t o 0.8 cm(-1)) spectral splitting for the case of OH-. We interpret the se two groups as the oscillations of two different pair-configurations : the first one from a pair of inequivalent molecular oscillators with crossed [100] orientations on next nearest [200] lattice sites with s trong elastic dipole interaction; the second one from a pair of equiva lent [100] oriented oscillators on nearest neighbor [110] sites, coupl ed by static electric dipole interaction and slightly split by dynamic coupling into ''in-phase'' and ''out-of-phase'' modes.