Parametric Resonance in the Drift Motion of an Ionic Bubble in near critical Ar Gas

The drift mobility of the negative oxygen ion in dense Argon gas near the liquid-vapor critical point has been measured as a function of the density. Near the critical temperature the zero-field density-normalized ion mobility shows a deep minimum at a density smaller than the critical one. This phenomenon was previously intepreted as the result of the formation of a correlated cluster of Argon atoms around the ion because of the strong electrostriction exerted by the ion on the highly polarizable and compressible gas. We now suggest that a possible alternative explanation is related to the onset of a parametric resonance of a bubble surrounding the ion. At resonance a large amount of energy is dissipated by sound waves in addition to viscous dissipation processes, resulting in the large mobility drop observed.