High-resolution x-ray-emission study of $1s4p$ and $1s3d$ two-electron photoexcitations in Kr

High-energy-resolution photoexcited $K{N}_{2,3}$ x-ray-emission measurements were carried out on krypton with the excitation energy tuned around the $1s4p$ and $1s3d$ double-excitation thresholds. Comprehensive two-dimensional resonant inelastic x-ray-scattering maps were recorded for the range of excitation and emission energies corresponding to both types of double excitations. The double-excitation signal could be clearly resolved from the dominant $1s$ ionization signal. The latter was subtracted from the measured maps, yielding isolated $1s4p$ and $1s3d$ photoexcitation spectra. Both two-electron excitation spectra are well described by a model spectrum built of consecutive bound-bound discrete transitions and shake-up and shake-off channels giving precise energies and intensities of the corresponding contributions. The obtained results are compared with other existing experimental values based on x-ray-absorption measurements and theoretical predictions.

Figure 1

(a) The difference between the Kr $K{N}_{2,3}$ emission spectra measured at two excitation energies (14 335.76 eV, black dashed line, and 14 382.26 eV, red solid line) below and above the $\left[1s4p\right]$ double-excitation threshold reveals a satellite structure on the high-energy tail of the diagram line (blue dash-dotted line). The two arrows indicate emission energies used to obtain the $K\text{−}N$ RIXS intensities presented in Fig. 2. (b) The theoretical $K{N}_{2,3}$ spectrum built from the calculated $\left[1s\right] {}^2{S}_{1/2}\text{−}\left[4p\right] {}^2{P}_{1/2}{,}^2{P}_{3/2}$ stick spectrum with a natural width of 2.71 eV [21] convoluted with the instrumental response is in perfect agreement with the spectrum measured below the $\left[1s4p\right]$ double-excitation threshold. (c) The calculated $[1s4p,4s]-[4p^2,4s4p]$ multiplet structure confirms the origin of the satellite which appears after tuning the excitation energy above the $\left[1s4p\right]$ double-excitation threshold.

Figure 2

Comparison of the recorded $K\text{−}N$ RIXS intensities as a function of the excitation energy with the emission analyzer fixed to 14 315.62 eV, corresponding to the maximum of the $KN-N^2$ satellite line, and to 14 311.07 eV, chosen symmetrically on the other (low-energy) side of the $K{N}_{2,3}$ diagram line.

Figure 3

The full $KN-N^2$ RIXS map of Kr. The color scale corresponds to the intensity of the final normalized counts after removing the $1s$ single-photoionization contribution.

Figure 4

The $K{N}_{2,3}$ PFY spectrum corrected for the decrease of the fluorescence yield ${\omega }_K$ above the $\left[1s4p\right]$ threshold compared with the reference absolute absorption cross section [13]. The comparison serves to provide the scaling factor used to convert the measured x-ray yields into absolute cross sections.

Figure 5

Comparison of the two emission spectra recorded below and above the $\left[1s3d\right]$ excitation threshold. A strong $KM$ satellite line superimposed on the tail of the $K{N}_{2,3}$ diagram line is observed when the excitation energy is tuned above the $\left[1s3d\right]$ threshold.

Figure 6

The full $KM-MN$ RIXS map of Kr. The color scale corresponds to the intensity of the final normalized counts after removing the $1s$ single-photoionization contribution.

Figure 7

Measured Kr $\left[1s4p\right]$ two-electron photoexcitation spectrum fitted with the model [red (gray) solid line] presented in the text. The inset presents the $KN$ satellite emission lines for three separate excitation energies (labeled with bars in the excitation spectrum) corresponding to discrete bound-bound, shake-up, and shake-off transitions (lines 1, 2, and 3, respectively). The individual emission spectra, which are shifted vertically for clarity, exhibit slight energy shifts.

Figure 8

Experimental Kr $\left[1s4p\right]nl{n}^{\prime }{l}^{\prime }$ resonant double-photoexcitation spectrum compared with the theoretical double bound-bound-transition cross section [13]. The original theoretical spectrum (dotted line) shifted by 2 eV (solid line) is in excellent agreement with the experiment.

Figure 9

Experimental Kr $\left[1s3d\right]$ double photoexcitation spectrum fitted with the model (red solid line) presented in the text. The spectrum is normalized to the high excitation energy part of the absolute experimental (dashed line) and theoretical (dotted line) absorption $\left[1s3d\right]$ cross sections from [13].