Free Volume Model Analysis of the O2- Ion Mobility in Dense Ar Gas

TL;DR

This study measures O2- ion mobility in dense argon gas across various temperatures and demonstrates that the thermodynamic Free Volume model, combined with slip correction, accurately describes ion transport from dilute to dense regimes.

Contribution

The paper applies and validates the thermodynamic Free Volume model for ion mobility in dense gases, extending its use from superfluid helium and neon to argon.

Findings

The FV model accurately predicts ion mobility across different densities.

Inclusion of the Millikan-Cunningham slip correction improves model fit.

Results confirm the model's universality for dense gas ion transport.

Abstract

We report the results of the experiment aimed at measuring the mobility of O2- ions in dense argon gas in the temperature range 180 K < T < 300 K. We show that an adequate theoretical description of the data is obtained by using the thermodynamic Free Volume (FV) model, originally developed to describe the electron bubble mobility in superfluid helium and successfully exploited for describing the O2- mobility in near critical neon gas. The model goal is to thermodynamically predict the free space available for ion motion. By implementing the FV model with the Millikan-Cunningham (MC) slip correction factor, we can describe the ion mobility in the crossover region bridging the dilute gas kinetic regime to the high-density hydrodynamic regime of ion transport. These results confirm the validity of the model and the universality of some of its features.