Theoretical determination of two-electron one-photon transition characteristics for low-$Z$ $K$-shell hollow atoms

Studying $K$-shell hollow atom spectra broadens our knowledge on femtosecond phenomena in atomic physics, chemistry, and biology. Recent synchrotron measurements of the two-electron one-photon (TEOP) transitions of low-$Z$ atoms have shown discrepancies between experiment and theoretical predictions of the TEOP relative intensities and their linewidths. The discrepancies seem to be a result of an incomplete description of an atomic response to the strong perturbation due to the $K$-shell double photoionization (DPI). A theoretical attempt, based on the multiconfiguration Dirac-Fock relativistic configuration interaction method, is presented for Mg, Al, and Si atoms. It is demonstrated that both the branching ratios and the TEOP linewidths can be closely reproduced by taking into account the influences of the core and valence electron correlations, open-shell valence configuration, and the outer-shell ionization and excitation processes following the $K$-shell DPI.

Figure 1

Level scheme (not to scale) showing the decay of $K$-shell hollow atoms via OEOP (blue arrows) and TEOP transitions (red arrows).

Figure 2

Comparison between theoretical end experimental branching ratios for Mg, Al, and Si. Experiment: Hoszowska et al. [3]; theory: Åberg et al. [26], Baptista [25], Saha et al. [27], “Kadrekar & Natarajan” means compilation of data from Ref. [10] and Ref. [44].

Figure 3

The “diagram” and OIE2-originating satellite contributions to the width of the $K\alpha {\alpha }^h$ line of Si.