The Extreme Ultraviolet Spectra of Scandium VI, Scandium VII and Other Elements Isoelectronic with Phosphorus I and Sulphur I

The spectra of Sc, Ti, V and Cr have been photographed in the region 80A to 700A with a large grazing incidence vacuum spectrograph. The irregular doublet law and constant second difference law have been used to aid in the identification of multiplets in ions of these elements. In the S I isoelectronic sequence, Sc VI multiplets involving the 3s²3p⁴³P, ¹D, ¹S-3s3p⁵³P⁰; 3s²3p³4s³S⁰, 1, 3D⁰, 1, 3P⁰ terms and the Ti VII multiplet involving the 3s²3p⁴³P-3s3p⁵³P⁰ terms have been observed. A number of intercombination lines have been identified, making possible an accurate calculation of the term values relative to the ground state. In the P I isoelectronic sequence, Sc VII multiplets involving the 3s²3p³⁴S⁰, ²D⁰, ²P⁰-3s²3p²4s⁴P, ²D, ²P and 3s3p⁴⁴P terms; Ti VIII multiplets involving the 3s²3p³⁴S⁰, ²D⁰, ²P⁰-3s²3p²4s⁴P, ²P, ²D terms; and V IX multiplets involving the 3s²3p³⁴S⁰, ²D⁰-3s²3p²4s⁴P, ²D terms have been observed. Since no intercombination lines have been observed it is impossible to assign relative term values to the doublet and quartet systems.