Critical Behavior of 2− Ions in Argon Gas

We measured the drift mobility of O2 ions in argon gas close to the critical point for (1.005 < T/TC < 1.04) above Tc* 150.7 K in the density range (0.025 Tc*. This anomalous reduction of ftgN occurs at a density Nm % 0.76Nc. We believe that this behavior is due to the strong electrostriction exerted by the ion on the highly compressible gas. By introducing suitable contributions to the effective ion radius R due to the large gas compressibility and taking into account short-range local density and viscosity augmentation due to electrostriction, the hydrodynamic Stokes formula fi0 = e/67i>]R, where rj is the gas viscosity, is in good agreement with the experimental data.