Editing Lyman-alpha (section)

==Fine structure==
[[image:Hydrogen fine structure2.svg|thumb|The Lyman-alpha doublet.]]
Because of the [[spin–orbit interaction]], the Lyman-alpha line splits into a [[fine structure|fine-structure]] doublet with the wavelengths of 1215.668 and 1215.674 angstroms.<ref>{{Citation| publisher = National Institute of Standards and Technology| last1 = Kramida| first1 = Alexander| last2 = Ralchenko| first2 = Yuri| title = NIST Atomic Spectra Database, NIST Standard Reference Database 78| accessdate = 2021-06-27| date = 1999| url = http://www.nist.gov/pml/data/asd.cfm}}</ref> These components are called Ly-α<sub>3/2</sub> and Ly-α<sub>1/2</sub>, respectively.

The eigenstates of the [[Perturbation theory (quantum mechanics)|perturbed]] [[Hamiltonian (quantum mechanics)|Hamiltonian]] are labeled by the ''total'' [[Angular momentum#Angular momentum in quantum mechanics|angular momentum]] ''j'' of the electron, not just the [[Azimuthal quantum number|orbital angular momentum]] ''l''. In the ''n''&nbsp;=&nbsp;2, ''l''&nbsp;=&nbsp;1 orbital, there are two possible states, with ''j''&nbsp;=&nbsp;{{sfrac|1|2}} and ''j''&nbsp;=&nbsp;{{sfrac|3|2}}, resulting in a spectral doublet. The ''j''&nbsp;=&nbsp;{{sfrac|3|2}} state has a higher energy and so is energetically farther from the ''n''&nbsp;=&nbsp;1 state to which it is transitioning. Thus, the ''j''&nbsp;=&nbsp;{{sfrac|3|2}} state is associated with the more energetic (having a shorter wavelength) spectral line in the doublet.<ref>{{Cite book |first=Bruce T. |last=Draine |year=2010 |title=Physics of the Interstellar and Intergalactic Medium |url=https://books.google.com/books?id=FycJvKHyiwsC&pg=PA83 |location=Princeton, N.J. |publisher=[[Princeton University Press]] |isbn=978-1-4008-3908-7 |oclc=706016938 |page=83}}</ref>