Anomalous isotope dependence of tunnel splitting of OH(-) and OD(-) defects in KCl and NaCl crystals.

We report low temperature high resolution Fourier-transform infrared stretching mode absorption and dielectric susceptibility measurements of OH(-) and OD(-) defects in potassium chloride and sodium chloride crystals. Although very low concentrated samples have been used in this investigation, we find in 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 exhibits a rather unusual isotope dependence, since the level splitting associated with the tunneling motion of the heavier defect ion OD- is larger than that due to OH- defects.