Thermodynamic Model for the Mobility of Oxygen Anions in Dense Neon Gas

Recently a thermodynamic model has been developed to describe and predict the ion mobility in He. It aims at computing the free volume available for the ionic drift motion through the medium. The radius of the free volume per particle is the hydrodynamic effective radius in the Stokes formula whose validity is extended to the region of large Knudsen number by using the Millikan-Cunningham slip factor correction. We used this model to describe new data of $\mathrm{O}_{2}^{-}$ ion mobility in supercritical Ne on several isotherms in a broad density range. The model parameters are adjusted once and for all by fitting the data on the isotherm closest to the critical one and allows the description of the density dependence of the mobility up to temperatures well above room temperature.