Editing Term symbol (section)

==Term symbols with ''LS'' coupling==
The usual atomic term symbols assume [[Angular momentum coupling#LS coupling|LS coupling]] (also known as Russell–Saunders coupling), in which the atom's total spin quantum number ''S'' and the total orbital angular momentum quantum number ''L'' are "[[good quantum number]]s". (Russell–Saunders coupling  is named after [[Henry Norris Russell]] and [[Frederick Albert Saunders]], who described it in 1925<ref>{{cite journal |last1=Russell |first1=H. N. |last2=Saunders |first2=F. A. |orig-date=January 1925 |title=New Regularities in the Spectra of the Alkaline Earths |url=http://adsabs.harvard.edu/full/1925ApJ....61...38R |access-date=December 13, 2020 |department=SAO/NASA Astrophysics Data System (ADS) |journal=Astrophysical Journal |year=1925 |language=en |publisher=adsabs.harvard.edu/ |volume=61 |page=38 |bibcode=1925ApJ....61...38R |doi=10.1086/142872 |via=harvard.edu}}</ref>). The [[spin-orbit interaction]] then couples the total spin and orbital moments to give the total electronic angular momentum quantum number ''J''. Atomic states are then well described by term symbols of the form:

{{Equation box 1 |indent=: |equation=<math>
^{2S+1}L_J
</math>|border colour = #50C878 |background colour = #ECFCF4}}
where
<ul>
<li>''S'' is the total [[spin quantum number]] for the atom's electrons. The value 2''S'' + 1 written in the term symbol is the [[Multiplicity (chemistry)|spin multiplicity]], which is the number of possible values of the spin magnetic quantum number ''M<sub>S</sub>'' for a given spin ''S''.</li>
<li>''J'' is the [[total angular momentum quantum number]] for the atom's electrons. ''J'' has a value in the range from |''L'' − ''S''| to ''L'' + ''S''.</li>
<li>''L'' is the total [[azimuthal quantum number|orbital quantum number]] in [[spectroscopic notation]], in which the symbols for ''L'' are:
{| style="text-align:center; line-height:110%; padding-left: 1em"
| style="width:2em" | ''L''&nbsp;=
| style="width:2em" | 0

| style="width:2em" | 1
| style="width:2em" | 2
| style="width:2em" | 3
| style="width:2em" | 4
| style="width:2em" | 5
| style="width:2em" | 6
| style="width:2em" | 7
| style="width:2em" | 8
| style="width:2em" | 9
| style="width:2em" | 10
| style="width:2em" | 11
| style="width:2em" | 12
| style="width:2em" | 13
| style="width:2em" | 14
| style="width:2em" | 15
| style="width:2em" | 16
| style="text-align:left; padding-left:0.25em;" | ...
|-
|
| {{serif|S}}
| {{serif|P}}
| {{serif|D}}
| {{serif|F}}
| {{serif|G}}
| {{serif|H}}
| {{serif|I}}
| {{serif|K}}
| {{serif|L}}
| {{serif|M}}
| {{serif|N}}
| {{serif|O}}
| {{serif|Q}}
| {{serif|R}}
| {{serif|T}}
| {{serif|U}}
| {{serif|V}}
| style="text-align:left; padding-left:0.25em;" | (continued alphabetically)<ref group="note">There is no official convention for naming orbital angular momentum values greater than 20 (symbol {{serif|Z}}) but they are rarely needed. Some authors use Greek letters (α, β, γ, ...) after {{serif|Z}}.</ref>
|}
</li>
</ul>

The orbital symbols S, P, D and F are derived from the characteristics of the spectroscopic lines corresponding to s, p, d, and f orbitals: [[sharp series|sharp]], [[Principal series (spectroscopy)|principal]], [[diffuse series|diffuse]], and [[fundamental series|fundamental]]; the rest are named in alphabetical order from G onwards (omitting J, S and P). When used to describe electronic states of an atom, the term symbol is often written following the [[electron configuration]]. For example, 1s<sup>2</sup>2s<sup>2</sup>2p<sup>2&nbsp;3</sup>P<sub>0</sub> represents the ground state of a neutral [[carbon]] atom. The superscript 3 indicates that the spin multiplicity 2''S'' + 1 is 3 (it is a [[triplet state]]), so ''S'' = 1; the letter "P" is spectroscopic notation for ''L'' = 1; and the subscript 0 is the value of ''J'' (in this case ''J'' = ''L'' − ''S'').<ref name=NIST>[http://physics.nist.gov/PhysRefData/ASD/levels_form.html NIST Atomic Spectrum Database] For example, to display the levels for a neutral carbon atom, enter "C I" or "C 0" in the "Spectrum" box and click "Retrieve data".</ref>

Small letters refer to individual orbitals or one-electron quantum numbers, whereas capital letters refer to many-electron states or their quantum numbers.