Experimental ion mobility measurements for the LCTPC collaboration—Ar-CF$_4$ mixtures

In this paper we present the results of the ion mobility measurements made in pure carbon tetrafluoride (CF$_4$) and gaseous mixtures of argon with carbon tetrafluoride (Ar-CF$_4$) for pressures ranging from 6 to 10 Torr (8–10.6 mbar) and for low reduced electric fields in the 10 Td to 25 Td range ($2.4-6.1 \text{kV} \cdot \text{cm}^{−1} \cdot \text{bar}^{−1}$), at room temperature. The time of arrival spectra revealed only one peak throughout the entire range studied which was attributed to CF$^+_3$. However, for Ar concentrations above 70%, a bump starts to appear at the left side of the main peak for reduced electric fields higher than 15 Td, which was attributed to impurities. The reduced mobilities obtained from the peak centroid of the time-of-arrival spectra are presented for Ar concentrations in the 5%–95% range.