In continuation of our previous work on doubly-excited ions with three and four electrons we present the first results on optical transitions in the term system of doubly-excited ions with five electrons. Transitions between such sextet states were identified in beam-foil spectra of the ions nitrogen, oxygen and fluorine. Assignments were first established by comparison with Multi-Configuration Dirac-Fock calculations. Later assignments were aided by Multi-Configuration Hartree-Fock calculations (see the contribution by G. Miecznik et al. in this issue). Decay curves were recorded for all six candidate lines. The lifetime results are compared to theoretical values which confirm most of the assignments qualitatively.

The C IV, N V, O VI and F VII quartet term systems have been investigated using the beam-foil method, Wavelengths of more than 70 lines associated with these systems are reported. They are compared to theoretical predictions and to data on analogous transitions in singly excited four-electron ions.Certain details of the term structure are discussed as are fine structure splittings and the separations of quartet terms arising from electron configuration 1s2p3p, 1s2p3d, and 1s2p4d. In the isoelectronic comparison the effect of configuration mixing becomes apparent for the last case.

The lifetimes of the resonance levels in the Al-like ions Ti X, Fe XIV and Ni XVI have been obtained from beam-foil measurements using a variety of analytical techniques. The spectral analysis and identification of cascade transitions necessary for application of the ANDC procedure have been aided by recent observations of laser-produced plasmas. The lifetime values obtained from ANDC analyses for the 3 s 3 p2 doublet levels agree well with predictions based on semi-empirical Hartree-Fock calculations. However, the ANDC results for the 3 s 2 3 d levels fall between the values obtained using multi-exponential curve-fitting and from the calculations.

Following an earlier observation in F VI we identified the line pair Is2s2p2 5p-Is2s2p3d 5p o , 5D o for the elements N, 0, Mg, and tentatively for Al and Si in beam-foil spectra. Assignment was established by comparison with Multi-Configuration Dirac-Fock calculations along the isoelectronic sequence. Using this method we also identified some quartet lines of lithiumlike ions with Z > 10.

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