Ionization of Gases

Ionization increases rapidly with voltage once these secondary processes take place, until ultimately breakdown occurs

1 / Ionization processes in gas discharges

The electrical breakdown of a gas is brought about by various processes of ionization.
These are gas processes involving the collision of electrons, ions and photons with

gas molecules, and electrode processes which take place at or near the electrode surface.

Relevant gas ionization processes

In the case of simple collision, the neutral gas molecule does not always get ionized on electron impact.
In such cases, the molecule will be left in an excited state M*, with energy Ee

Ionization by Double electron impact

If a gas molecule is already raised to an excited state (with energy Ee) by a previous collision, then ionization of this excited molecule can occur by a collision with a relatively slow electron