Mobility of O$_2^-$ ions in supercritical Ar: Experiment and Molecular Dynamics Simulations

TL;DR

This study combines experimental measurements and molecular dynamics simulations to analyze how O$_{2}^{-}$ ion mobility in supercritical argon varies with temperature and density, revealing a defect near the critical point.

Contribution

It provides new experimental data and MD simulation insights into ion mobility behavior in supercritical gases, especially near the critical temperature.

Findings

Mobility depends strongly on temperature and density.

A mobility defect occurs below the critical density.

Simulations accurately reproduce the mobility defect near $T_c$.

Abstract

A new analysis and new Molecular Dynamics (MD) simulations of the measurements of the mobility $\mu_{i}$ of O$_{2}^{-} $ ions in dense supercritical Ar gas are reported. $\mu_{i}$ shows a marked dependence on the distance from the critical temperature $T_{c}.$ 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 $T_{c}.$