Microwave spectroscopy of the KCl:Li+system: The standard model

The paraelectric resonance of KCl:${\mathrm{Li}}^{+}$ (both ${}_{}{}^6{}_{}{}^{}\mathrm{Li}_{}^{+}{}_{}{}^{}$ and ${}_{}{}^7{}_{}{}^{}\mathrm{Li}_{}^{+}{}_{}{}^{}$) was investigated in the presence of hydrostatic pressure for a wide range of microwave frequencies and electric fields. The results are interpreted in terms of the standard 〈111〉-tunneling model and provide the most stringent test of this model to date. The agreement is excellent and above approximately 500 bars we can determine the three distinct tunneling parameters for this system. These parameters increase dramatically with pressure, while the electric dipole moment decreases with pressure. We compare our data with various theoretical predictions.