Ionic mobilities in liquid xenon

The drift mobility of positive ions of tetramethylsilane (TMSi) and of negative oxygen ions in liquid xenon was measured as a function of temperature from 161 K (triple point) to 205 K. The mobility of the TMSi⁺ ion is more than one order of magnitude lower than the intrinsic mobility of positive charge carriers (holes) in very pure liquid xenon. The positive ionic mobility is influenced by electrostrictive effects, which lead to the formation of solid layers of Xe atoms around the ion, and to a locally enhanced viscosity. A simple model for the cluster formation is discussed. Qualitative agreement is obtained over most of the temperature range, but serious deviations occur at the triple point. Another shortcoming of the model is the fact that it cannot explain the higher mobility of the negative oxygen ions