Spectrograms of 208Pb electrodeless discharge tubes operated in a field of 24025 gauss gave Zeeman patterns for fifty-eight PbI spectral transitions from 2189 to 10969 Å and yielded eighteen new g values. There was good agreement between these and the g values predicted by intermediate-coupling eigenvectors determined from least-squares level fitting. The g value of the odd level at 58517 cm−1 indicates that it belongs to the 6p6d configuration instead of 6s6p3 as formerly classified.
A striking consequence of configuration interaction has been discovered which results in the total suppression of what would otherwise be a strong line in this spectrum. A predominantly 6p6d level is mixed with 6p7s and interference between the dipole matrix elements connecting respectively the 6d and 7s portions with a ground-state level causes a net dipole moment of almost exactly zero for this transition. However, even in our relatively weak magnetic field, this balance is upset by magnetic mixing of only 0.3% with a third level to enhance the line strength by at least a factor 106! Two related transitions with normal pattern separations display pronounced anomalies in the relative intensities of their Zeeman components. We give a theoretical analysis and quantitative calculations to show that these anomalies are due to combined interference effects of the two types of mixing.
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