Arc Spectrum of Lead*

New grating and interferometric measurements of the first emission spectrum of lead have been made using electrodeless discharge tubes containing halides of 208Pb. In the spectral region from 1977 to 12561 Å, 370 classified lines were measured, of which 90 are new. Nineteen new even levels and four new odd levels have been established; the classifications of nine levels have been changed to different electron configurations. The lower series limit of lead was determined from three Rydberg series to be 59819.4 ± 0.3 cm−1, and the separation of the two limits, 14081.074 ± 0.004 cm−1, was measured directly from the forbidden Pb ii transition, 6pP122−6pP322.A series of hydrogenic levels observed by Gieseler and Grotrian in 1925 but omitted from AEL was confirmed for n = 5 to 9 and extended to n = 10. We have identified this as the 6png1/2[7/2]3 series of levels, the observed lines being forbidden Δl = 3 transitions to the J = 2 members of the 6p2 and 6p7p configurations. This is believed to be the first ng series identified in a two-electron neutral spectrum. In addition to the formerly observed even-even forbidden transitions between individual members of the 6p2 ground configuration, we also observed such transitions to 6p2 from 6p7p and 6p5f levels.