Mobility of 02 ions in near critical Ar gas

We have measured the drift mobility μ of O2 in Ar gas in the temperature range (151.5 < T < 157.0) K near Tc (150.86 K) and in the density range (2 < N < 140) X 1026 atoms/m3 around Nc (80.8 × 1026 atoms/m3). We have observed a strong reduction of the zero-field density-normalized mobility rμ0N as T → Tc but for N < Nc. We suggest that this reduction is due to the effect of the long-range ion-atom polarization interaction and of the divergence of the gas compressibility. A satisfactory agreement with the data can be obtained by suitably modifying the Stokesʹs hydrodynamic expression for μ0.