What is the cause for the fine structure? I know that it describes the splitting of the spectral lines of atoms but I don't understand its cause, any help is appreciated
When we observed the emission spectrum of hydrogen, we were able to see a fine splitting in the spectrum. This was something where Bohr's model of atom failed to explain. This was arising due to the interaction of the intrinsic spin of the electron with the magnetic field created by the orbital motion of the electron around the atom. The angular momentum of electrons the units of reduced plank's constant is 1/2. this has only 2 possible
Stern-Gerlach experiment showed (space quantization) direction either parallel or antiparallel to the magnetic field of the atom. Which increases or decreases the energy of the electron. Hope this solved your doubt.