Quartet terms in the arc spectrum of copper

The arc spectrum of copper, in common with the spectra of other elements in the first group of the Periodic Table has been shown to contain a system of doublet series. The chief lines of copper were classified by Rydberg and by Kayser and Runge. Some additional combinations were discovered by Dunz and the series have since been re-tabulated by Fowler. Only one member of the principal series of copper has been identified with certainty, though Fowler gives five members of the diffuse and six members of the sharp series. An interesting feature of the series system of copper is the occurrence of a somewhat abnormal term, designated as X, which combines with the two members of the doubletp level, forming the well-known doublet λ 5700·25, λ 5782·16. The nature of the combination with the doublet terms, and the Zeeman effect, showed the X-term to be a doubletd term with inner quantum number 2. It was to be expected that this term would have a companion term with inner quantum number 3, but the earlier investigators failed to find this term. The identity of the missing term has been made clear in a recent paper by Shenstone who gives the numerical value of the term as 51105·5, the value of 51105·0 having previously been suggested by Ruark and by Werner. The numerical value of the term X is given by Fowler as 49062·6. It follows that the differenced 3 —d 2 ** = 2042·9 and the completed —p doublet includes the line λ 5105·55.