<p>I am going through the theory of <a href="https://en.wikipedia.org/wiki/Saha_ionization_equation" rel="nofollow noreferrer">Saha equation</a> but I am not able to understand the concept of ionisation state? What are ionization states actually?</p>

CC BY-SA 3.0
2016-05-18T13:18:06.603Z
I guess this question is more appropriate at physics.SE, but briefly: It's the degree to which an atom — or an ensemble of atoms — is ionized. That is, is it missing one, two, three, etc. electrons. But beware: Whereas chemists, and normal physicists I think, use the notation (with iron as an example) Fe, Fe$^{+1}$, Fe$^{+2}$, Fe$^{+3}$, etc. for neutral, singly-ionized, and doubly-ionized, triply-ionized iron, astronomers use Fe I, Fe II, Fe III, Fe IV, etc. That is, [astronomers' Roman number] = [chemists Arabic number] + 1.
pela
CC BY-SA 3.0
2016-05-30T00:04:01.037Z
The comment by Pela is the correct answer. Astronomers needed a way to designate the neutral or un-ionized state.
TazAstroSpacial
CC BY-SA 4.0
2019-04-06T18:45:29.827Z
@pela In fact, this goes to Chemist SE (ionizing atoms).
User123
<astrophysics><spectroscopy>
What is meant by ionization states?
Rian
# What is meant by ionization states?

(Asked by: username_0 on 2016-05-18)

I am going through the theory of [Saha equation](https://en.wikipedia.org/wiki/Saha_ionization_equation) but I am not able to understand the concept of ionisation state? What are ionization states actually?

**Tags:** astrophysics, spectroscopy
> **Comments:**
> **username_1**: I guess this question is more appropriate at physics.SE, but briefly: It's the degree to which an atom — or an ensemble of atoms — is ionized. That is, is it missing one, two, three, etc. electrons. But beware: Whereas chemists, and normal physicists I think, use the notation (with iron as an example) Fe, Fe$^{+1}$, Fe$^{+2}$, Fe$^{+3}$, etc. for neutral, singly-ionized, and doubly-ionized, triply-ionized iron, astronomers use Fe I, Fe II, Fe III, Fe IV, etc. That is, [astronomers' Roman number] = [chemists Arabic number] + 1.  
> **username_2**: The comment by Pela is the correct answer. Astronomers needed a way to designate the neutral or un-ionized state.  
> **username_3**: @pela In fact, this goes to Chemist SE (ionizing atoms).  

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