Mobilities and longitudinal diffusion coefficients for K+ ions in nitrogen and argon

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Abstract
We have constructed a drift tube with a movable ion source and measured the mobilities and longitudinal diffusion coefficients for K+ ions at 303 °K in N2 and at 305 °K in Ar in the pressure range 0.3–5.0 Torr, over the E/N range 4–346 Td in N2 and 3–320 Td in Ar. The zero-field reduced mobilities for K+ ions in N2 and Ar were determined to be 2.50±0.03 and 2.63±0.03 cm2/V sec, respectively. Both values are in excellent agreement with the values reported by Elford and Milloy. When our data are compared with the values obtained by Thomson et al. in N2 and the values obtained by James et al. in Ar over the entire E/N range, we find that the mean deviations are about 1.7%, independent of gas species and E/N. Our zero-field reduced mobilities are about 1.2% lower in both cases than the values compiled by Ellis et al. It is concluded that the discrepancy is due to a systematic error and is not caused by clustering reactions. The mean values of NDL over the E/N range 4–7 Td in N2 and 5–10 Td in Ar were found to be 1.96×1018 and 2.09×1018 cm−1 sec−1, respectively. Both values are about 7% higher than the values calculated from our mobility data by the generalized Einstein relation and from the same parameters reported by Pai et al.