Monte Carlo simulation of O2− ion transport and rate properties in noble gases with O2 addition

Abstract

The kinetics of O2− ions were numerically studied in He and Ar with a small admixture of O2 in a strong electric field through a Monte Carlo simulation. Cross sections for elastic scattering between O2− ions and He and Ar atoms were determined by adjusting cross section values to obtain good agreement between calculated and measured ion mobilities in pure helium and argon. Ion transport coefficients, mean energy, and detachment rate were calculated for various mole fractions of O2 and values of the reduced electric field. It was shown that the O2− ion mobility, mean energy, and detachment rate in He:O2 mixtures are much higher than those in Ar:O2 mixtures and air. A great difference between the properties of O2− ions in He–O2 and Ar–O2 mixtures was explained on the basis of the difference in the polarizability and mass for He and Ar atoms. Calculated detachment rates can be used for simulating guided ionization waves in He and Ar flows ejected into ambient air.