NEW SPECTROSCOPIC RESULTS IN THE 2S2P5-2S2P43S TRANSITION ARRAY OF MG-4+, AL-5+ AND SI-6+ IONS

Experimental and theoretical results on far UV transitions between levels of configurations 2s2p43s and 2s2p5 in Mg V, Al VI and Si VII spectra are reported. Theoretical analysis by means of ab initio and semi-empirical methods leads to a new identification of a number of lines, nine of which pertain to the Si VII spectrum. These are situated in the 70-90 AA range, and have not been observed previously. The energy levels of the upper configurations of Al5+ and Su6+ ions are calculated in the intermediate coupling scheme. The correlation effects expressed by configuration interactions do not greatly influence the relative energy position of the analysed lines but they do have significant consequences on their relative intensities.