Collisional electron detachment and decomposition rates of SF−6, SF−5, and F− in SF6: Implications for ion transport and electrical discharges

Abstract

Measured cross sections for prompt collisional detachment and decomposition of SF⁻₆, SF⁻₅, and F⁻ in SF₆ reported in the preceding companion paper are used to calculate detachment coefficients and ion‐conversion reaction coefficients as functions of electric field‐to‐gas density ratio (E/N) for ion drift in SF₆. Analysis from a model presented here using these coefficients suggests that prompt electron detachment from SF⁻₆ and SF⁻₅ in SF₆ are insignificant processes in such ion‐drift experiments. Calculated rates for ion‐conversion processes indicate the necessity to: (1) reexamine the previously measured rates in SF₆ from drift‐tube experiments, and (2) use ion kinetic‐energy distributions with larger high‐energy tails than the standard distributions assumed in earlier calculations. The calculated detachment and reaction coefficients are used in a model which invokes detachment from long‐lived energetically unstable states of collisionally excited SF⁻₆ to explain the pressure dependence of previously measured detachment coefficients and the high detachment thresholds implied by analysis of electrical‐breakdown probability data for SF₆. Consistent with the interpretation of results from earlier work, the model indicates that at high pressure, measured detachment coefficients depend primarily upon rates for ion conversion and prompt collisional detachment from F⁻.