Measurement and analysis of the photoabsorption spectra of laser-produced Al and in the region of 2p-subshell excitation

The 2p-subshell photoabsorption spectra of atomic aluminium and singly ionized silicon, measured using the dual-laser plasma technique, are presented. The spectra are dominated by and one- and two-electron excitations, respectively. Relative photoabsorption cross sections, derived from the experimental spectra, are compared with computed theoretical cross sections. An interpretation is provided within the framework of the Hartree-Fock configuration-interaction calculations. It is found that mixing between core singly and doubly excited configurations strengthens with increasing atomic number at the beginning of the aluminium isoelectronic sequence. This observation is in contrast to our findings for the Mg-like isoelectronic species Mg, and (Sayyad M H et al 1995 J. Phys. B: At. Mol. Opt. Phys. 28 1715) in which such mixing weakens with increasing atomic number.