The 2p-subshell absorption spectrum of Al III

The photoabsorption spectrum of Al III has been observed in the 175-120 AA (571 000-833 000 cm -1 ) spectral region, using the continuum radiation emitted by a laser-produced plasma as a background source. All the observed transitions involve the excitation of a 2p-subshell electron. The electron configuration of the upper levels is of the type 2p 5 3snd or 2p 5 3sns. A critical analysis of the spectrum is made with the help of multiconfigurational relativistic atomic structure calculations. It is found that the 2p 5 3p 2 configuration acts as a strong perturber and that there is departure from LS coupling for many of the terms. Lines belonging to the transition array 2p 6 3p to 2p 5 3s3p were also observed.