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...
We review the Bohr atomic model, where certain conditions (quantum conditions) were used to select certain "allowed" circular orbits for the electrons in an atom. Sommerfeld realized that a more generalized condition, applied to the action variables, would be consistent with the Bohr condition and...