Hello.
I'm now trying to make Argon plasma discharge simulation. In order to do this, I need to know cross section of Argon for various reaction (ionization, excitaiton and etc) with incident electron. When I looked at some table of reactions, It seems that the table distinugishes excitation state of Argon into resonant state and metastable state. The symbol of the resonant state is Ar^(*) and Ar^(*m) is for the metstable state.
What are them? what is difference between two states?
And I don't know what sort of notation is used to express excitation states in the attached image. Could you tell me what it is and how to read? Any studying material for the notation is also welcome!
Metastable states are those state that do not decay radiatively. In argon is the triplet state for example. Because this state can decay only by collision, it survive a very long time. I do not know what resonant states are, I guess, that there is e resonant electron induced transitions coupling these states to the ground state, and therefore the cross section is very high.
The first excited state is the argon metastable, Use NIST database to find the correspondence between state configuration and energy.
For a collisional radiative model of Argon please look at the paper of Vlecek and Bogaerts.
Oh thanks! At least I got to know what the metastable state is. I'm surprising that there is excited states which do not radiatively decayed, only decayed by collision.
Can I have one more question? Could you tell me anything about why the triplet state in argon is metastable? How doesthe triplet states correlate with the metastable?
The triplet state is metastable because the triplet to singlet transition is "forbidden", meaning that it has a 0 (or very close to 0) probability of relaxing radiatively. So, the most likely way for it to relax is via collision with another atom or molecule.
Am...I'll try to be familar with selection rule again (although I stuided this in Q.M class in old time) but I'm afraid that it take a little time so this question is lagged behind by new questions.
Could you briefly give me how the selection rule is applied so that triplet to singlet transition is clearly seen as not allowed in math?
Dear Jang,
I am not going to repeat the good explanations from the colleagues above. Concerning simulation of Argon plasma please take into account that it strongly depends on the type of discharge. Usually, all low temperature plasmas are non-equilibrium and the EEDF is non-Maxwellian. It is important to chose appropriate Ar levels diagram (only first 4s and elementary processes for a given discharge conditions. In order to obtain correct cross sections for the processes you would need to find the actual EEDF and to integrate the cross-sections with it. Using Maxwellian EEDF or rate coefficient obtained from the literature at other conditions can give you absolutely different incorrect results.
If you are interested, you can check papers J. Appl. Phys. 84 (1998) 147; Phys. Rev. E 60 (1999) 875; J. Appl. Phys. 87 (2000) 7652; Vacuum 76 (2004) 409. In some of them the reactions and their cross-sections can be found.
For more information please do not hesitate to contact me.
Evgenia
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