The Zeeman effect in the two strongest mixed multipole lines of neutral bismuth was studied with apparatus of high resolving power and magnetic fields up to 6400 G. Remarkable differences of intensity distribution among the ΔM = ±1 components, caused by interference between the magnetic-dipole and the electric-quadrupole radiation, are found for the two directions of observation (longitudinal L and transverse π). This interference effect was observed for the first time in a spectrum with hyperfine structure. In stronger fields, the transitions investigated are of the type ΔM = MF′-M″, where M″ = MJ″+MI″; the individual components belonging to various MF′ and MI″ formed unresolved groups. For the line 4615 Å(2P°½ → 4S°3/2), the sum of the interference terms decreases the intensities of groups with MJ″ = ±3/2 and increases the intensities of groups with MJ″ = ±½ in the L direction; the reverse is true for the transverse π direction. The line 6476 Å (2D°5/2 → 4S°3/2) exhibits the opposite behavior. In spite of the complex, and to a great extent unresolved, detailed structure of the Zeeman pattern at low as well as at high fields, the observations of finer details seem to support the expectation that coupling of the J vector to the nuclear moment I does not destroy, but only modifies, the interference terms so that they operate on the individual hyperfine-structure components.
J. HELDT and S. MROZOWSKI, "Interference Effect in Mixed Multipole Lines of Bi I," J. Opt. Soc. Am. 60, 467-474 (1970)