The spectrum of a hollow-cathode discharge in a mixture of phosphorus vapor and helium has been hotographed and measured from 500–10 000 A. This source gave new lines of P II and a much more complete P I spectrum than has hitherto been observed. The P II spectrum of 401 lines is essentially classified by combinations of 38 even and 54 odd levels. Thirty-six of these levels are new, and 29 previously listed levels have been rejected. The 3s2 3p 3d, 4d, 4p, 4ƒ, and 3s3p3 configurations are now complete. Several 5d and 6s levels and most of the expected 5p levels have been found. Except for 3s3p3 and 3s23p · nd, which how interaction, the configurations are in good agreement with first-order Russell-Saunders theory. The P II ionization potential is 19.72 v. The previous analyses of P I have been revised and extended to include 98 even and 43 odd levels classifying 382 of 490 lines. New terms belonging to the configurations 3s2 3p24–7s, 4–6p, 3–7d and 4,5ƒ have been found. Wherever feasible, the results have been confronted with the predictions of theory. Several series allow the calculation of a new ionization potential, which is 10.484 v.
WILLIAM C. MARTIN, "Atomic Energy Levels and Spectra of Neutral and Singly Ionized Phosphorus (P I and P II)," J. Opt. Soc. Am. 49, 1071-1084 (1959)