{c}

In the Paschen-Back effect, the external <magnetic field> interaction becomes large compared with the <spin-orbit interaction> that holds $\mathbf L$ and $\mathbf S$ coupled. Then $J$ ceases to be a good approximate <quantum number>; $m_L,m_S$ become more useful, with leading electronic shifts $\Delta E\simeq\mu_BB(m_L+g_sm_S)$. In the ideal complete-decoupling limit an <electric-dipole interaction> preserves $m_S$, so its <spin> contribution cancels between the levels and orbital triplet spacing can reappear. Intermediate fields require mixing the coupled states. This is a change of coupling regime, distinct from the weak-field <anomalous Zeeman effect>; still larger fields require additional terms beyond this linear model.


 Paschen-Back effect (source code)