Mobilities of Negative Ions in SF6

Abstract

Mass identified mobilities were measured at 300°K for negative ions formed by a pulsed spark discharge in SF6. Zero field mobilities of the four ion species, SF5−, SF6−, SF6−(SF6), and SF6−(SF6)2, were found to be 0.595 ± 0.007, 0.542 ± 0.007, 0.470 ± 0.010, and 0.420 ± 0.010 cm2 V−1·sec−1, respectively. The SF6−(SF6)2 ion was observed to be collisionally destroyed at E / n values greater than 100 × 10−17 V·cm2. The present data indicate that the zero field mobility of 0.570 cm2 V−1·sec−1 previously reported by McAfee and Edelson and by McDaniel and McDowell may have referred to the unresolved SF5−1 and SF6− ions. All four mobilities measured in this experiment are significantly below the predictions of the Langevin mobility theory in its polarization limit.