Super-Coster-Kronig decay of Kr $3p$ core-hole states studied by multielectron coincidence spectroscopy

Super Coster-Kronig (SCK) decay following Kr $3p$ photoionization has been investigated using a multielectron coincidence method. It is found that the SCK pathway occupies 23% of the $3p_{1/2}$ decay and only 2.5% of the $3p_{3/2}$ decay. The significant difference between the two $3p$ spin-orbit levels mainly results from the difference in energetics: almost all SCK transitions are energetically allowed in the $3p_{1/2}$ decay but only SCK transitions to the ${}^{3}F$ levels of $3d^{-2}$ are possible in the $3p_{3/2}$ decay. Subsequent decay processes from the SCK-final $3d^{-2}$ states are investigated, where a maximum of fivefold electron coincidences are analyzed.

Figure 1

Electron detection efficiency estimated from yields of coincidence between Ar $2p$ photoelectrons and the associated Auger electrons. Experimental values (black circles) were fitted with a double exponential decay function (solid red curve). Intensities in Figs. 2, 3, and 5, 6, 7 were corrected for the detection electron efficiency (see text for details).

Figure 2

(a) Inner-shell photoelectron spectrum of Kr at a photon energy of 355.2 eV, plotted in 0.2-eV steps. The two kinetic energy ranges for the extractions of coincidence events relevant to the $3p_{3/2}$ and $3p_{1/2}$ decays are indicated. (b) Two-dimensional map showing energy correlation between photoelectrons in the same range as in (a) and Auger electrons in the kinetic energy range of 0–120 eV. Color represents number of coincidences found in a box with dimensions of 0.4 eV (vertical) × 0.6 eV (horizontal).

Figure 3

Coincidence Auger spectra associated with the individual spin-orbit components of $3p^{-1}$: (a) whole range and (b) low kinetic energy portion. They are plotted with 0.1-eV steps. In the derivation of the spectra in (b), only the coincidence events including two additional electrons in the 0–60-eV kinetic energy range are used, in order to concentrate the contribution from the SCK transitions. In the extractions of the spectra in Figs. 5, 6, 7, the electrons in the energy ranges indicated in (b) were assumed to be SCK electrons. The pink-shaded curve, which is obtained by subtracting half the intensity of the $3p_{3/2}$ Auger spectrum from the $3p_{1/2}$ Auger spectrum, delineates the net SCK contribution in the $3p_{1/2}$ Auger spectrum. A fitting with the sum of seven Lorentzian peaks, whose widths and locations are fixed at the $3p_{1/2}$ natural width and at the estimated locations of the $3d^{-2}$ levels, respectively, is shown.

Figure 4

Energy levels of Kr ion states lying below 240 eV, where energetically crowded levels are simplified. The numbers indicate the branching ratios (in %) of the decay pathways from the $3p^{-1}$ states, where the values for the $3p_{1/2}$ and $3p_{3/2}$ decays are written in red and blue, respectively.

Figure 5

Two-dimensional map showing subsequent decay of $3d^{-2}$ states populated by SCK transitions from $3{p_{1/2}}^{\text{–}1}$. Correlations between ${\mathrm{Kr}}^{3+}3d^{\text{–}1}4l^{\text{–}2}$ states formed from $3d^{-2}$ and the energy of slow Auger electrons emitted in further decay are shown. The map was derived from fourfold coincidences including a $3p_{1/2}$ photoelectron and an electron in the SCK electron range (2–12.5 eV) indicated in Fig. 3. Colors represent number of coincidences found in a box with dimensions 0.17 eV (vertical) × 0.17 eV (horizontal). The top panel shows the spectrum of the energy sum of $3p$ photoelectron, SCK electron, and faster Auger electron. This spectrum delineates structures of ${\mathrm{Kr}}^{3+}3d^{\text{–}1}4l^{\text{–}2}$ states formed from $3d^{-2}$, when the faster Auger electron is emitted in the initial Auger decay from $3d^{-2}$ states. The step size is 0.1 eV.

Figure 6

Same as in Fig. 5, but for the $3p_{3/2}$ decay. The map was derived from fourfold coincidences including a $3p_{3/2}$ photoelectron and an electron in the SCK electron range (0–3 eV) indicated in Fig. 3.

Figure 7

(a) Histograms of the kinetic energy sum of the five electrons including a $3p_{1/2}$ or $3p_{3/2}$ photoelectron, which is plotted in steps of 0.07 eV. (b) Energy distributions of electrons ejected upon the formation of ${\mathrm{Kr}}^{5+}4p^{\text{–}5}$ levels. The range of the kinetic energy sum, selected to derive these distributions, is indicated in (a). The step size is 0.025 eV.