The ionization is the action which consists to remove or add loads to a Atome or a Molécule. The atom - or the molecule - while losing or by gaining loads is not neutral any more electrically. It is then called Ion.

The applications are numerous:

• food decontamination
• modifications of the plastics
• sterilization of the medical devices
• study of the materials
• etc

Energy of the first ionization

It is energy necessary to extract the first electron (i.e. the electron whose binding energy is weakest) of the atomic structure.

Formulate generic describing ionization with an electron: $X\; -\; >\; X^+\; +\; e^-$

Electronic impact

This type of ionization is usually used in Spectrométrie of mass. An electron emitted by a filament meets the atom or the molecule and tears off to him at the time of the shock one of its electrons (Spectrometry mass).

Example with methane: $CH\_4\; +\; e^-\; -\; >\; CH4^++\; +\; 2e^-$

Photoionization

Ionization can be realized by radiations sufficient wavelength to eject this outer-shell electron. When the ionizing ray consists of photons, one speaks about photoionization. It is for example what occurs in the planetary nebulas.

Thermal ionization

If one brings sufficient thermal energy to a gas, its average energy can become equal or higher than its energy of ionization. The components of this gas can thus ionize under the shocks between atom/molecule. It is what arrives in the solar crown.

The average energy of a perfect gas is equal to $\backslash \; frac\; \{3\}\; \{2\}\; kT$, or more precisely à$\backslash \; frac\; \{1\}\; \{2\}\; kT$ per degree of liberté.
$k$ corresponds to the Boltzmann constant.
$T$ corresponds to the temperature.

Chemical ionization

It is a reaction between a molecule and a réactant ion. The result will give place has a transfer of proton or to the creation of Adduit.

Example with a molecule $M$:
$M\; +\; CH\_5^+\; -\; >\; MH^+\; +\; CH\_4$

See too

• Ionizing ray
• Spectrometry mass
• Ionization of the food
• Plasma

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