Spin-Orbit Coupling
A relativistic quantum interaction between an electron's intrinsic spin magnetic moment and the internal magnetic field created by its orbital motion around the nucleus.
Governing formula
H_SO = ξ(r) L · S
SI unit
eV (Energy Shift)
In depth
In the electron's rest frame, the moving charged nucleus produces an internal magnetic field. Interaction between electron spin S and orbital angular momentum L shifts atomic energy levels, splitting degenerate levels into fine structure.
Examples in the real world
Splitting the yellow sodium emission spectrum into two distinct lines (589.0 nm and 589.6 nm doublet).