Photoionization of Mg and Ar isonuclear sequences

Photoionization of the $2s$ inner shell of several atomic systems belonging to the Mg $\left(Z=12\right)$ and Ar $\left(Z=18\right)$ isonuclear sequences (Mg, ${\text{Mg}}^{2+}$, ${\text{Mg}}^{8+}$, Ar, ${\text{Ar}}^{6+}$, ${\text{Ar}}^{8+}$) is investigated using the relativistic random-phase approximation and also the relativistic random-phase approximation modified to include the relaxation of atomic core. Comparison of results obtained using these two approximations reveals an important effect of relaxation, namely, that inner-shell photoionization, particularly for neutral atoms and low-charge ions, can be quite sensitive to the removal of outer electrons, contrary to what is generally believed.

Figure 1

(a) Photoionization cross sections for $2s$ subshell of Mg, ${\text{Mg}}^{2+}$, and ${\text{Mg}}^{8+}$: the vertical solid lines are the DF thresholds and dotted lines are the corresponding $\Delta E_{SCF}$ thresholds given in Table . (b) Magnified view of (a).

Figure 2

(a) Photoionization cross sections for $2s$ subshell of Ar, ${\text{Ar}}^{6+}$, and ${\text{Ar}}^{8+}$: the vertical solid lines are the DF thresholds and dotted lines are the corresponding $\Delta E_{SCF}$ thresholds given in Table . (b) Magnified view of (a).