Penning ionization is a form of chemi-ionization, an ionization process involving reactions between neutral atoms and/or molecules. The process is named after the Dutch physicist Frans Michel Penning who first reported it in 1927. The Penning effect is put to practical use in applications such as gas-discharge neon lamps and fluorescent lamps, where the lamp is filled with a Penning mixture to improve the electrical characteristics of the lamps.
Penning ionization refers to the interaction between a gas-phase excited-state atom or molecule G* and a target molecule M resulting in the formation of a radical molecular cation M+., an electron eâˆ’, and a neutral gas molecule G:
G* + M -> M+â€¢ + e- + G
G* + M -> MG+â€¢ + e-
Surface Penning ionization refers to the interaction of the excited-state gas with a surface S, resulting in the release of an electron.
G* + S -> G + S + e-
(The positive charge symbol â€ªS +â€¬ that would appear to be required for charge conservation is omitted, because S is a macroscopic surface and the loss of one electron has a negligible effect.) Wikipedia, Penning Ionization