New measurements and identifications of the transitions 3s 23pk -3s3p k+1 have been made in the spectra of S IV, K IV-VII, Ca V-VIII, Sc VI-IX, Ti VII-X, V VII-XI, Cr VIII-XI, Mn IX-XI, and Fe X, XI. The energy parameters of the ground configurations have been determined and expressed as functions of Z by semi-empirical formulae in the S I, P I, Si I, and Al I isoelectronic sequences. Predicted wavelengths for some 150 forbidden lines of astrophysical interest are tabulated.

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Improved level values for 3s 23p 53d and 3s 2 3p 4 3d of Fe IX and Fe x are derived from the observed forbidden lines with special regard to recent accurate measurements in the vacuum-ultraviolet part of the coronal spectrum. A procedure for estimating expected relative intensities is proposed and used for an additional check on the consistency of the identifications, which now comprise 12 lines of Fe IX and 11 lines of Fe x. Finally, by use of a suitable extrapolation technique the wavelengths of corresponding lines in nickel are predicted, which leads to some new identifications and a total of 6 identified lines of Ni xI and 4 of Ni xII.

The spectrum of three times ionized calcium emitted from sliding spark discharges has been observed using 3-m normal incidence spectographs and a 2-m Ebert spectograph. More than 500 lines have been identified in the wavelength region 295 A to 2830 A as combinations between 106 levels of the configurations 3s' 3p5, 3s3p6, 3$ 3p43d, 4s, 4p, 4d, 5s and 3s3ps 3d. The level structure has been theoretically interpreted by means of calculations including configuration interactions. Energy parameters determined from leastsquares fits to the observed level values are compared with theoretical values obtained with Hartree-Fock wavefunctions from the Cowan computer code.

The spectrum of four times ionized scandium emitted from a sliding spark discharge has been observed using a 3 m normal incidence spectrograph and a 5 m grazing incidence spectrograph. About 450 lines in the wavelength region 160 A to 2200 A have been identified as combinations between 46 odd levels belonging to the 3s23ps, 3s23p4 4 p and 3s3p5 3d configurations and 1 2 even levels of the 3s3p6, 3s23p4 3d, 4d, 4s and 5s configurations. Of the previous identifications we have confirmed 18 levels. The level structure of the observed configurations has been theoretically interpreted by including configuration interaction effects. The inclusion of 3s23p3 3d2 in the calculations of the odd parity configurations is found to be important. Almost all levels of 3s3p5 3d show a considerable mixing with levels of 3s23p33dZ, in some cases by as much as 50%. The energy parameters determined from least-squares fits to the observed level values are compared with Hartree-Fock calculations. The ionization energy is estimated to be 739 500 -f lOOOcm-'. (91.65 i 0.12eV).