The limiting condition for sparkover in gases forming unstable negative ions

The theory predicting the limiting E/p (electric field strength/gas pressure), below which uniform-field breakdown is not possible, is extended to cover those electronegative gases where unstable negative ions are effective. The result is consistent with the experimental results of other authors in oxygen. It is shown that in general at the limiting E/p the growth of current with distance is not linear, in contrast to the case where only stable negative ions are formed.