Hi Ibrahim--
It would help if you provided more information.
For example,it is very difficult to have a gas of pure lithium that you ionize...Please see the link I attached.
Best,
--Keith
@KeithDPatch
http://www.chemguide.co.uk/atoms/properties/ies.html
First of all you should clarify what do you mean for ionization temperature. It is the temperature where ionization degree becomes 1?
Obviously metal atoms are the more easily ionized gas, but you will add the evaporation energy. At the end, almost all the pure gases existing has similar ionization energy.
Anyway there is not a direct correspondence between ionization energy and temperature, because the heat capacity determine how much energy you should put to ionize the gas.
In the general case of molecular gas, you have to account for excitation of vibration, then dissociation and then ionization. While atomic system must account only for electronic excitation, which usually is very close to ionization.
Let us consider O2. The energy to produce 1 electron is about 12 eV to O2+ and 16 to O+ (dissociation first). In equilibrium, the concentration of O2+ is always small, because dissociation is favored, and ion with large concentration is usually O+, except at very very high pressure.
Anyway, these considerations are valid only for thermal plasmas. In non-equilibrium conditions the behavior is different, and strongly depends on the way you are furnishing energy to the gas.
Let us compare oxygen with He, which ionization energy is about 24 eV.
Just comparing the different ionization energies, one should say that it is easier to create a plasma in oxygen. This is wrong! And there are different reasons for that. First of all the O2 is an electron-negative gas and therefore electron attachment is an important source of electron loss. Secondly, the vibrational excitation slow down the heating of the electrons, reducing the probability of ionization.
Hope it helps
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