Penning ionization

The Penning ionization (also Penning effect called) is a special form of Chemoionisation , that is a transfer of excitation energy in particle collisions. The effect is named after the Dutch physicist Frans Michel Penning , who described it in 1927.

mechanism

If excited atoms of one type of particle appear in a gas mixture , the excitation energy of which is greater than the ionization energy of the second type of particle , then in the event of a collision the excitation energy can be transferred from to M in such a way that it is ionized. The mechanism has not yet been fully uncovered. However, one explanation would be the formation of an intermediate stage: ${\ displaystyle G}$ ${\ displaystyle M}$ ${\ displaystyle G}$ ${\ displaystyle M}$

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

This intermediate stage does not always have to decay; ionizations of the following types are also possible:

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

In addition, surface Penning ionization can be observed at gas-solid interfaces . The mechanism behind this is that of the Augerabregung (Auger deexcitation): ${\ displaystyle S}$

{\ displaystyle G ^ {*} + S \ to G + S ^ {+} + e ^ {-}}

application

In practice, the effect is used with gas discharge lamps . The lamp is filled with a so-called Penning mixture in order to reduce the operating voltages (e.g. the ignition voltage ). A frequently used Penning mixture is, for example, a mixture of 98 to 99.5% neon with 0.5-2% argon . Neon has an excitation energy of approx. 16.6 eV, argon an ionization energy of 15.8 eV. The mixture is easier to ionize than neon or argon alone, since the ionization balance of the discharge is improved through the additional use of excitation energy.

Individual evidence

↑ FM Penning: About ionization through metastable atoms . In: The natural sciences . tape 15 , no. 40 , 1927, pp. 818-818 , doi : 10.1007 / BF01505431 .
↑ Manfred von Ardenne (ed.): Effects of physics and their applications. Harri Deutsch Verlag, 2005, ISBN 3-8171-1682-9 , p. 264 ( limited preview in Google book search).
^ Metastable Impact Electron Spectroscopy. Clausthal University of Technology , accessed on September 22, 2017 .

[1] FM Penning: About ionization through metastable atoms . In: The natural sciences . tape 15 , no. 40 , 1927, pp. 818-818 , doi : 10.1007 / BF01505431 .

[2] Manfred von Ardenne (ed.): Effects of physics and their applications. Harri Deutsch Verlag, 2005, ISBN 3-8171-1682-9 , p. 264 ( limited preview in Google book search).

[3] Metastable Impact Electron Spectroscopy. Clausthal University of Technology , accessed on September 22, 2017 .