Clustering of Negative Ions in Oxygen

Observed transient ion currents in oxygen below breakdown at low $\mathrm{pd}$ deviate from those predicted by use of the assumption that ions are formed during the initiating electron pulse and retain their identity while drifting in the electric field. The deviations, ascribed to clustering reactions that generate ${\mathrm{O}}_2^{-}$ and ${\mathrm{O}}_3^{-}$ from initially formed ${\mathrm{O}}^{-}$, are analyzed to obtain values for the clustering rates. These rates have orders of magnitude comparable with ionization and attachment rates under the experimental conditions. Their variation with $\frac{E}{p}$ and $p$ are discussed and possible clustering reactions are suggested.