fine structure
The various corrections to the energy levels of hydrogen are shown schematically. The gap between the n = 1 and n = 2 shells is supressed, and the Lamb and hyperfine shifts are exaggerated in comparison with the fine-structure.
Fine structure is closely spaced lines in part of the spectrum of a given element; a familiar example are the D lines of sodium. Fine structure results from the interaction between electrons in an atom and the atom's own magnetic field, which splits the various energy levels into a number of near-spaced sublevels.
See also spin.
