Penning ionization

The Penning ionization ( also called Penning effect) 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

Stepping into a gas mixture excited atoms of a particle type G, whose excitation energy is greater than the ionization energy of the second particle type M, then in a collision, the excitation energy of G be transferred to such M that M is ionized. The mechanism is not completely revealed. However, an explanation would be the formation of an intermediate stage:

This intermediate does not always fall apart, it is also possible ionizations of the following type:

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

Application

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