Mobility of O2 ions in supercritical Ar: Experiment and Molecular Dynamics Simulations

A new analysis and new Molecular Dynamics (MD) simulations of the measurements of the mobility μi of O − 2 ions in dense supercritical Ar gas are reported. μi shows a marked dependence on the distance from the critical temperature Tc. A mobility defect appears as a function of the gas density and its maximum value occurs below the critical density. The locus of points of maximum mobility defect in the P − T plane appears on the extrapolation of the coexistence curve into the single-phase region. MD simulations quantitatively reproduce the mobility defect near Tc.