Penning ionization

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Penning ionization is a form of chemi-ionization, an ionization process involving reactions between neutral atoms or molecules.[1][2] The process is named after the Dutch physicist Frans Michel Penning who first reported it in 1927.[3] 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 e, and a neutral gas molecule G:[4]

G^* + M \to M^{+\bullet} + e^- + G

Penning ionization occurs when the target molecule has an ionization potential lower than the internal energy of the excited-state atom or molecule.


Associative Penning ionization can also occur:

G^* + M \to MG^{+\bullet} + e^-

Surface Penning ionization (Auger Deexcitation) refers to the interaction of the excited-state gas with a surface S, resulting in the release of an electron:

G^* + S \to G + S + e^-

The positive charge symbol S^+ 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.

See also[edit]


  1. ^ Arango CA, Shapiro M, Brumer P (2006). "Cold atomic collisions: coherent control of penning and associative ionization". Phys. Rev. Lett. 97 (19): 193202. arXiv:physics/0610131. Bibcode:2006PhRvL..97s3202A. doi:10.1103/PhysRevLett.97.193202. PMID 17155624. 
  2. ^ Hiraoka K, Furuya H, Kambara S, Suzuki S, Hashimoto Y, Takamizawa A (2006). "Atmospheric-pressure Penning ionization of aliphatic hydrocarbons". Rapid Commun. Mass Spectrom. 20 (21): 3213–22. doi:10.1002/rcm.2706. PMID 17016831. 
  3. ^ Penning, F. M. Die Naturwissenschaften, 1927, 15, 818. Über Ionisation durch metastabile Atome.
  4. ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version:  (2006–) "Penning gas mixture".