L-photoionization of atomic aluminium: production of Al II, Al III and Al IV UV lines

Abstract

Aluminium atoms undergoing soft X–ray irradiation produce multiply–ionized ions in excited states through inner–shell photoionization followed by radiationless transitions, i.e. Auger cascades. Photoionization of 2s–, 2p – and 3s subshells are considered for the 80 eV to 1 keV incident photon energy range. Photoionization cross sections, shake probabilities and Auger and Coster–Kronig rates are evaluated in various proximations. Alii, Al iii and Al iv UV lines are directly produced independently of local temperature and electron density. Monopole shake up/off and conjugate shake up excitations are important over a large energy interval beyond the L thresholds.