Editing Hydrogen (section)

==== Electron energy levels ====
{{Main|Hydrogen atom}}
The [[ground state]] [[energy level]] of the electron in a hydrogen atom is −13.6&nbsp;[[Electronvolt|eV]],<ref>{{cite web|author1=NAAP Labs|title=Energy Levels|url=http://astro.unl.edu/naap/hydrogen/levels.html|publisher=University of Nebraska Lincoln|access-date=20 May 2015|date=2009|archive-url=https://web.archive.org/web/20150511120536/http://astro.unl.edu/naap/hydrogen/levels.html|archive-date=11 May 2015|url-status=live}}</ref> equivalent to an [[ultraviolet]] [[photon]] of roughly 91&nbsp;nm wavelength.<ref>{{cite web|url=http://www.wolframalpha.com/input/?i=photon+wavelength+13.6+ev|title=photon wavelength 13.6 eV|access-date=20 May 2015|date=20 May 2015|work=Wolfram Alpha|archive-url=https://web.archive.org/web/20160512221720/http://www.wolframalpha.com/input/?i=photon+wavelength+13.6+ev|archive-date=12 May 2016|url-status=live}}</ref> The energy levels of hydrogen are referred to by consecutive [[quantum number]]s, with <math>n=1</math> being the ground state. The [[hydrogen spectral series]] corresponds to emission of light due to transitions from higher to lower energy levels.<ref>{{Cite book |last=Levine |first=Ira N. |title=Quantum chemistry |date=1970 |publisher=Pearson |isbn=978-0-321-89060-3 |edition=2 |series=Pearson advanced chemistry series |location=Boston}}</ref>{{rp|105}} Each energy level is further split by [[spin (physics)| spin]] interactions between the electron and proton into 4 [[Hyperfine_structure|hyperfine]] levels.<ref>{{Cite book |last1=Feynman |first1=Richard P. |url=https://www.worldcat.org/title/671704374 |title=The Feynman lectures on physics |last2=Leighton |first2=Robert B. |last3=Sands |first3=Matthew L. |date=2011 |publisher=Basic Books |isbn=978-0-465-02414-8 |edition=New millennium |location=New York |chapter=The Hyperfine Splitting in Hydrogen |oclc=671704374 |chapter-url=https://www.feynmanlectures.caltech.edu/III_12.html}}</ref> 

High precision values for the hydrogen atom energy levels are required for definitions of physical constants. Quantum calculations have identified 9 contributions to the energy levels. The eigenvalue from the [[Dirac equation]] is the largest contribution. Other terms include [[Relativistic quantum mechanics|relativistic]] recoil, the [[self-energy]], and the [[vacuum polarization]] terms.<ref>{{Cite journal |last1=Tiesinga |first1=Eite |last2=Mohr |first2=Peter J. |last3=Newell |first3=David B. |last4=Taylor |first4=Barry N. |date=2021-09-23 |title=CODATA Recommended Values of the Fundamental Physical Constants: 2018* |journal=Journal of Physical and Chemical Reference Data |volume=50 |issue=3 |pages=033105 |doi=10.1063/5.0064853 |issn=0047-2689 |pmc=9888147 |pmid=36726646|bibcode=2021JPCRD..50c3105T }}</ref>