Zeeman to Paschen-Back crossover

What you are seeing: the 2p levels of hydrogen as a function of magnetic field $B$ . At weak fields the splitting is $g_J m_J \mu_B B$ (Zeeman). At strong field $\mathbf L$ and $\mathbf S$ decouple and the splitting becomes $(m_L + 2 m_S) \mu_B B$ (Paschen-Back). Crossover occurs when Zeeman energy equals fine-structure energy.

Figure 1. Energy splitting from weak to strong

B

B (T)2.00

WHAT TO TRY

Vary each control and watch the rail readouts respond.
Compare the diagnostic plot against the live scene.