Sommerfeld's extension of Bohr's atomic model was motivated by the quest for a theory of the Zeeman and Stark effects. The crucial idea was that a spectral line is made up of coinciding frequencies which are decomposed in an applied field. In October 1914 Johannes Stark had published the ...
The additional magnetic field causes changes of the angular momentum and hence shifts of the energy of the atomic levels. We study this effect for the cases of the Zeeman effect, where the source is an external homogeneous magnetic field, and the hyperfine interaction, where the source is the...