A paraelectric system with two electric dipole moments: KI: OH−

Paraelectric resonance in KI: O${\mathrm{H}}^{-}$ at 1.5 and 4.2°K has been measured from 12 to 150 GHz, using a combination of fixed- and swept-frequency techniques. The data confirm the existence of a low-lying excited multiplet of energy levels 140 GHz above the ground-state multiplet and a simple two-multiplet tunneling model is shown to be in good agreement with the main features of the experimental data. The dipole moment of O${\mathrm{H}}^{-}$ in the ground-state multiplet is 1.25 $e$ Å, and 2.15 $e$ Å in the excited multiplet, while the dipole orientation in each is $〈110〉$. The nearest-neighbor tunneling parameters are dominant, having magnitudes of 8.25 and 13.5 GHz in the lower and upper multiplets, respectively, with a small admixture of second-nearest-neighbor tunneling. The observation of a second multiplet has been interpreted as evidence for a coupled dipole system in which the intrinsic dipole moment of O${\mathrm{H}}^{-}$ and the off-center dipole moment can combine in several ways. The swept-frequency experiments, in addition to providing an accurate measurement of some zero-field splittings, show that the absorption line shape is symmetric in frequency at low electric fields. This result implies that internal-electric-field broadening is not a dominant contribution to the linewidths observed in this system.