Negative ion motion in mixtures of CH/sub 4/ and Ar with low SF/sub 6/ content

This paper deals with the measurement of the mobility of negative ions in the mixture SF/sub 6/-CH/sub 4/-Ar, with SF/sub 6/ contents of up to 50%. The Pulsed Townsend Technique was used to produce electronic and ionic avalanches over the low E/N range in which ionization is either negligible or absent, and attachment processes are significant. The E/N range of measurement was 1 to 100 Td. The structure of the measured signals strongly suggests that there is only one negative ion, most likely formed by resonant attachment. A test of the measured mobilities with Blanc's law provides further support to ascribe the drifting species to SF/sub 6//sup -/.