Fine Structure
The small splitting of atomic spectral lines resulting from relativistic mass corrections and spin-orbit coupling.
Governing formula
E_fine ~ α² E_n, α ≈ 1 / 137
SI unit
eV (Energy Splitting)
In depth
Fine structure splits spectral lines by a factor proportional to the square of the fine-structure constant α ≈ 1/137. It is accurately predicted by the relativistic Dirac equation.
Examples in the real world
Splitting hydrogen spectral lines into closely spaced multiplets observable with high-resolution spectrometers.