Experimental ion mobility measurements in Ar-CO₂ mixtures

In this paper we present the experimental results for the mobility of ions in argon-carbon dioxide gaseous mixtures (Ar-CO₂) for pressures ranging from 6 to 10 Torr and for reduced electric fields in the 10 Td to 25 Td range, at room temperature.The time-of-arrival spectra of the several mixture ratios studied revealed that the relative abundance of the ions and their mobilities depend on the mixture ratio. For Ar concentrations below 80% only one peak was observed in the spectra which was attributed to CO₂⁺, while for Ar concentrations above 80% a second peak appears at the left side of the main peak, which may be due to impurities, probably H₂O⁺. In this work, the time-of-arrival spectra from which reduced mobilities were obtained for Ar concentrations of 20% (K₀ = 1.141±0.004 cm²V⁻¹s⁻¹), 50% (K₀ = 1.385±0.009 cm²V⁻¹s⁻¹), 85% (K₀ = 1.690±0.022 cm²V⁻¹s⁻¹) and 95% (K₀ = 1.954±0.043 cm²V⁻¹s⁻¹) are displayed as well as other reduced mobilities values obtained similarly. The ion mobility study was performed at reduced electric field values typically used in gaseous detectors.