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 3<i>s</i><sup>2</sup> 3<i>p</i> 3<i>d</i>, 4<i>d</i>, 4<i>p</i>, 4ƒ, and 3<i>s</i>3<i>p</i><sup>3</sup> configurations are now complete. Several 5<i>d</i> and 6<i>s</i> levels and most of the expected 5<i>p</i> levels have been found. Except for 3<i>s</i>3<i>p</i><sup>3</sup> and 3<i>s</i><sup>2</sup>3<i>p</i> · <i>nd</i>, 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 3<i>s</i><sup>2</sup> 3<i>p</i><sup>2</sup>4–7<i>s</i>, 4–6<i>p</i>, 3–7<i>d</i> 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)