Hydrogenic fine-structure levels
For a spin-one-half electron bound to an infinitely heavy point nucleus of charge +Ze, the binding energy through order (Zα)⁴ is E_nj≈−m_ec²(Zα)²/(2n²)−m_ec²(Zα)⁴[n/(j+½)−¾]/(2n⁴), with α=e²/(4πε₀ħc).
Key knowledge
For a spin-one-half electron bound to an infinitely heavy point nucleus of charge +Ze, the binding energy through order (Zα)⁴ is E_nj≈−m_ec²(Zα)²/(2n²)−m_ec²(Zα)⁴[n/(j+½)−¾]/(2n⁴), with α=e²/(4πε₀ħc). The leading Coulomb degeneracy is split by j while states with the same n,j remain degenerate in this approximation.
Values and equations
E_nj≈−m_ec²(Zα)²/(2n²)−m_ec²(Zα)⁴[n/(j+½)−¾]/(2n⁴); α=e²/(4πε₀ħc)
- E_nj
- Binding energy relative to rest energy J
- m_e
- Electron mass kg
- c
- Vacuum light speed m s⁻¹
- e
- Positive elementary-charge magnitude C
- ε₀
- Vacuum permittivity F m⁻¹
- ħ
- Reduced Planck constant J s
- Z,n,j,l,α
- Dimensionless nuclear charge, quantum numbers and coupling
Conditions and scope
- Positive integer Z, principal n≥1, allowed orbital l≤n−1 and total j=l±1/2 with only j=1/2 for l=0; Zα≪1 and energy measured relative to electron rest energy.
- Includes kinetic, spin–orbit and Darwin corrections for the stated external point-Coulomb model. Lamb shift, hyperfine, finite size and finite nuclear-mass/recoil corrections lift or shift further levels and are outside this formula; simply replacing m_e everywhere by a reduced mass is not a complete recoil treatment.
Sources · 2
References
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Evidence and review
Quantum Physics III: chapter 2, fine structure: §2.1 printed page 25 allows e²→Ze² in the Coulomb potential; §2.4.1–§2.4.3 and equations 2.4.59–2.4.63, printed pages 36–43, sum all three corrections and give the n,j energy. Hydrogenic powers follow the same Coulomb scale substitution; α is converted from Gaussian e²/(ħc) to SI. Quantum Mechanics (2016): Energy levels of a hydrogen atom: Equations 11.196–11.199: point-Coulomb Dirac energy and its small-α expansion; subtract the rest-energy term. Excludes the source's description of n as radial rather than principal quantum number.
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