Auger Shake-Up Assisted Electron Recapture

The presence of doubly excited states (DESs) above the core-hole ionization threshold nontrivially modulates the x-ray absorption because the participator Auger decay couples DESs to the underlying low-energy core-hole continuum. We show that coupling also affects the high-energy continuum populated by the spectator Auger decay of DESs. For the $K-L_{23}^2$ Auger decay of the $1s^{-1}3p^{-1}4s^2{}^{1}P$ state in argon, the competing nonresonant path is assigned to the recapture of the $1s$ photoelectron caused by emission of the fast electron from the shake-up $K-L_{23}^2$ decay of the $1s^{-1}$ ion.

Figure 1

The electronic transition scheme following photon absorption in the region of $1s^{-1}3p^{-1}4s^2$ DESs in argon. $V_{Rc}$ denotes amplitude of the $R\to 1s^{-1}\epsilon p$ participator Auger decay to the low-energy continuum. The spectator Auger decay (red arrow) couples $R$ to the high-energy $2p^{-2}3p^{-1}nl{n}^{\prime }{l}^{\prime }\epsilon (s,d)$ continuum, which is populated also by the Auger shake-up assisted photoelectron recapture from the low-energy continuum (dotted red arrow, $c_{fg}$ amplitude). The dashed (blue) arrows and the black arrow mark the $K-M$ x-ray decay and the diagram $K-L_{23}^2$ Auger decay, respectively. The kinetic energies of the $1s$ photoelectron and of the resonant and nonresonant $K-L_{23}^2$ electrons are denoted by ${\epsilon }_p$, ${\epsilon }_f$, and ${\epsilon }_A$, respectively. For clarity, the $K-L$ decay is omitted.

Figure 2

The $K(M)-L_{23}^2(M)$ electron yield of Ar measured at 3219.4 eV (red dotted curve) and 3222.4 eV (black curve) photon energy. The inset shows the RA line emitted by the $1s^{-1}3p^{-1}4s^2$ atomic resonance and two weak ${{}^{3}P}_{2,0}$ nonresonant Auger lines emitted in decay of the $1s^{-1}$ state. The corresponding theoretical RA spectrum (gray curve) is shifted and scaled to match the observed position and intensity of the observed RA line, respectively. The bars show relative contributions of final states to an angle-integrated RA spectrum. Label $F$ denotes a group of final states giving rise to the RA line.

Figure 3

(a) The measured absorption spectrum (black dots) in the region of the $1s^{-1}3p^{-1}nl{n}^{\prime }{l}^{\prime }$ DES in Ar [12]. According to the semiclassical estimate [see Eq. (9) in Ref. [4] ], the recapture more likely occurs due to emission of faster $K-L^2$ Auger electrons (black curve) than slower $L-M^2$ Auger electrons (black dotted curve) at the same asymptotic kinetic energy of photoelectron. (b) The $K(M)-L_{23}^2(M)$ electron yield in the vicinity of resonance $R$ leading to final states $F$ after subtracting the tail of the $2p^{-2}{{}^{1}D}_2$ diagram Auger line. The RA line shows a linear dispersion (black line), while the position of the weak $2p^{-2}{{}^{3}P}_0$ diagram line is independent of photon energy (dashed line).

Figure 4

The three faces of the $1s^{-1}3p^{-1}4s^2$ resonance in Ar. (a) The resonance profile constructed from x-ray yield of the $K-M_{23}$ satellite line (black points), fitted by the Lorentzian (blue curve) [12]. (b) The profile constructed from the electron yield of the $K-L_{23}^2$ satellite line $F$ (black points), fitted by Eq. (1) (red curve). The comparison is made with the calculated CIS, considering (black curve) and not considering (black dashed curve) the interferences with DES neighbors. The dotted black curve presents the calculated contribution of resonance $R$. (c) The absorption spectrum (black points) fitted by the sum (green curve) of the Fano profile and the noninteracting continuum background [see Eq. (a5) in the Appendix]. The extrapolated background of the unperturbed $1s\epsilon p$ photoionization without (black curve) and with added contribution of the higher-lying resonances (black dotted curve) are also plotted.