For 10 points, name this splitting of spectral lines in a magnetic field.
Mössbauer spectroscopy involves the observation of phenomena including isomer shifts and this.  An equation describing it contains an electron spin g-factor of approximately two. It was first observed by its namesake in the D lines of sodium and its anomalous variety occurs when electron spin contributes to this phenomenon. A potential energy associated with it is proportional to the Bohr magneton, the Lande g-factor, and the z component of the total momentum. This is the magnetic analog to the Stark effect, and in strong fields it becomes the Paschen-Back effect. The inverse type of it considers absorption lines as opposed to spectral lines. For 10 points, name this splitting of spectral lines in a magnetic field.
Mössbauer spectroscopy involves the observation of phenomena including isomer shifts and this.  
{Zeeman} Effect