Photoionization of atomic aluminium in the region from 80 to several hundred eV leads to emission of a number of Al II, Al III and Al IV lines. Relative intensities of all the emission lines change as the incident photon energy increases due to opening of channels for various processes, like single photoionization, shake up or shake off processes.
Monopole and conjugate shake up, shake off and double shake off processes upon photoionization, as well as similar processes upon Auger and Coster-Kronig decay of the states produced by photoionization, play an important role in line emission.
Low-intensity Al II 3s3p-3s2 is emitted due to 3s-photoionization which is not negligible in the energy range of interest.
2p-photoionization is the principal producer of Al III line emission. The most intense line emitted upon single 2p-photoionization is Al III 3p-3s 1857 Å UV line. A number of other Al III lines are emitted due to double processes upon 2p-photoionization. Their intensities are roughly one order of magnitude less.
The single 2s-photoionization gives rather little emission since the 2s-vacancy decays non-radiatively into ionic ground states. On the other hand, the shake off processes upon 2s-photoionization contribute to Al IV emission.
Acknowledgements
AGK would like to thank his colleagues from Laboratoire Cassini UMR 6529 for their hospitality during his stay in Nice. This work was partly supported by the fundamental research grant from Russian Ministry of Railway Transport (No 510(9)/2001)
Copyright ESO 2002