Weak spin-forbidden Paschen-Back line
= Weak spin-forbidden Paschen-Back line
{title2=$I_{\rm weak}\propto(\beta/\mu_BB)^2$}
At large but finite <magnetic field>, opposite-spin admixtures in approximate product <eigenstates> let nominally spin-forbidden electric-dipole channels borrow <intensity>. Their amplitudes scale as <spin-orbit interaction> <energy> divided by Zeeman <energy>; their intensities therefore vanish quadratically in that ratio.