imported>LR.127: Adding short description: "Format for notating atoms and molecules"

2024-12-27T01:53:39Z

Adding short description: "Format for notating atoms and molecules"

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{{Short description|Format for notating atoms and molecules}}
{{About-distinguish2|the notation for atomic and molecular orbitals|the [[Russel–Saunders term symbol]], a similar notation that describes multi-electron systems, which is often referred to as "spectroscopic notation" as well}}

'''Spectroscopic notation''' provides a way to specify atomic [[ion|ionization states]], [[atomic orbital]]s, and [[molecular orbital]]s.

==Ionization states==
[[Spectroscopists]] customarily refer to the spectrum arising from a given ionization state of a given [[chemical element|element]] by the element's symbol followed by a [[Roman numeral]]. The numeral I is used for spectral lines associated with the neutral element, II for those from the first ionization state, III for those from the second ionization state, and so on.<ref>p. 92, ''Guide to the Sun'', Kenneth J. H. Phillips, Cambridge, UK: Cambridge University Press, 1992. {{ISBN|0-521-39788-X}}.</ref> For example, "He I" denotes lines of neutral [[helium]], and "C IV" denotes lines arising from the third ionization state, C<sup>3+</sup>, of [[carbon]]. This notation is used for example to retrieve data from the [http://physics.nist.gov/PhysRefData/ASD/levels_form.html NIST Atomic Spectrum Database].

==Atomic and molecular orbitals==
Before [[atomic orbitals]] were understood, spectroscopists discovered various distinctive series of spectral lines in atomic spectra, which they identified by letters. These letters were later associated with the [[azimuthal quantum number]], ''ℓ''. The letters, "s", "p", "d", and "f", for the first four values of ''ℓ'' were chosen to be the first letters of properties of the spectral series observed in [[alkali metals]]. Other letters for subsequent values of ''ℓ'' were assigned in alphabetical order, omitting the letter "j"<ref>§12-7, ''An Introduction to Quantum Physics'', Anthony Philip French and Edwin Floriman Taylor, CRC Press, 1979. {{ISBN|0-7487-4078-3}}.</ref><ref>§7.12, [http://astrowww.phys.uvic.ca/~tatum/stellatm.html ''Stellar Atmospheres''], [[Jeremy B. Tatum]], online book. Accessed on line September 19, 2007.</ref><ref name="hp" /> because some languages do not distinguish between the letters "i" and "j":<ref>[https://books.google.com/books?id=QbQJAgAAQBAJ&pg=PA106] P.Atkins et al. ''Quanta, Matter, and Change: A Molecular Approach to Physical Chemistry'' (Oxford University Press) p.106</ref><ref>W.C. Martin and W.L. Wiese (2002), Atomic, Molecular, and Optical Physics Handbook (version 2.2). [Online] Available: https://www.nist.gov/pml/atomic-spectroscopy-compendium-basic-ideas-notation-data-and-formulas/atomic-spectroscopy-11 [2021, May 12]. National Institute of Standards and Technology, Gaithersburg, MD.</ref>
:{| class="wikitable"
|- align="center"
! width="40px" | letter !! name !! width="30px" | ''ℓ''
|- align="center"
| s || align="left" | '''s'''harp || 0
|- align="center"
| p || align="left" | '''p'''rincipal || 1
|- align="center"
| d || align="left" | '''d'''iffuse || 2
|- align="center"
| f || align="left" | '''f'''undamental || 3
|- align="center"
| g
|
| 4
|- align="center"
| h
|
| 5
|- align="center"
| i
|
| 6
|- align="center"
| k
|
| 7
|- align="center"
| l
|
| 8
|- align="center"
| m
|
| 9
|- align="center"
| n
|
| 10
|- align="center"
| o
|
| 11
|- align="center"
| q
|
| 12
|- align="center"
| r
|
| 13
|- align="center"
| t
|
| 14
|- align="center"
| u
|
| 15
|- align="center"
| v
|
| 16
|- align="center"
| ...
|
| ...
|}

This notation is used to specify [[electron configurations]] and to create the [[term symbol]] for the [[electron]] states in a multi-electron atom. When writing a term symbol, the above scheme for a single electron's [[azimuthal quantum number|orbital quantum number]] is applied to the total orbital angular momentum associated to an electron state.<ref name="hp">[http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/hydcol.html#c3 Spectroscopic notation], web page at http://hyperphysics.phy-astr.gsu.edu/, accessed on line September 19, 2007.</ref>

===Molecular spectroscopic notation===
{{main|Molecular term symbol}}
The spectroscopic notation of molecules uses Greek letters to represent the modulus of the orbital angular momentum along the internuclear axis.
The quantum number that represents this angular momentum is Λ.

: Λ = 0, 1, 2, 3, ...
: Symbols: Σ, Π, Δ, Φ

For Σ states, one denotes if there is a reflection in a plane containing the nuclei (symmetric), using the + above. The − is used to indicate that there is not.

For homonuclear diatomic molecules, the index g or u denotes the existence of a [[Molecular symmetry#Elements|center of symmetry]] (or inversion center) and indicates the symmetry of the [[vibronic spectroscopy|vibronic]] wave function with respect to the point-group inversion operation '''''i'''''. Vibronic states that are symmetric with respect to '''''i''''' are denoted g for {{lang|de|gerade}} (German for "even"), and unsymmetric states are denoted u for {{lang|de|ungerade}} (German for "odd").

== Quarkonium ==
For [[meson]]s whose constituents are a heavy [[quark]] and its own antiquark ([[quarkonium]]) the same notation applies as for atomic states. However, uppercase letters are used.

Furthermore, the first number is (as in nuclear physics) <math>n = N+1</math> where <math>N</math> is the number of nodes in the radial wave function, while in atomic physics <math>n = N+\ell+1</math> is used. Hence, a 1P state in quarkonium corresponds to a 2p state in an atom or [[positronium]].

==See also==
{{cmn|colwidth=30em|
* [[Azimuthal quantum number]]
* [[Electron configuration]]
* [[List of chemistry mnemonics#Atomic orbital|Mnemonics for orbital letters]]{{Broken anchor|date=2024-06-06|bot=User:Cewbot/log/20201008/configuration|target_link=List of chemistry mnemonics#Atomic orbital|reason= The anchor (Atomic orbital) [[Special:Diff/678044300|has been deleted]].}}
* [[Principal quantum number]]
* [[Term symbol]]
* [[X-ray notation]]
* [[Molecular symmetry]]
}}

==References==
{{reflist}}

[[Category:Atomic physics]]
[[Category:Spectroscopy]]

Spectroscopic notation - Revision history

imported>LR.127: Adding short description: "Format for notating atoms and molecules"