Anomalous isotope dependence of tunnel splitting of OH- and OD- defects inKCl and NaCl crystals

We report low temperature high resolution Fourier-transform infrared stretc hing mode absorption and dielectric susceptibility measurements of OH- and OD- defects in potassium chloride and sodium chloride crystals. Although ve ry low concentrated samples have been used in this investigation, we find i n all cases significant deviations from the behavior expected for isolated tunneling defects. The most interesting result is the observation that the tunneling of hydroxide and deuteroxide defects in both host crystals exhibi ts a rather unusual isotope dependence, since the level splittings associat ed with the tunneling motion of the heavier defect ion OD- is larger than t hat due to OH- defects.