# Single photon core ionization with core excitation: a new spectroscopic tool

F Penent, S Carniato, P Lablanquie, P Selles, J Palaudoux, L Andric, M Žitnik, K Bučar, E Shigemasa, M Nakano, et al.

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F Penent, S Carniato, P Lablanquie, P Selles, J Palaudoux, et al. Single photon core ionization with core excitation: a new spectroscopic tool. Journal of Physics: Conference Series, 2015, 635 (11), pp.112093 10.1088/1742-6596/635/11/112093. [https://doi.org/10.1088/1742-6596/635/11/112093](https://doi.org/10.1088/1742-6596/635/11/112093). [arXiv:1503.01367](https://arxiv.org/abs/1503.01367)

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Single photon core ionization with core excitation: a new spectroscopic tool

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2015 J. Phys.: Conf. Ser. 635 112093

(http://iopscience.iop.org/1742-6596/635/11/112093)

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Single photon core ionization with core excitation: a new spectroscopic tool.

Penent F.*<fnref n="1" />, Carniato S.*², Lablanquie P.*, Selles P.*, Palaudoux J.*, Andric L.*, Žitnik M.&, Bučar K.&, Shigemasa E.£, Nakano M.†, Hikosaka Y.† and Ito K.†

**Synopsis.** The simultaneous core ionization and core excitation process (or K⁻²V process) induced by absorption of a single photon provides the basis of a new spectroscopy that offers both advantages of X-ray Photoelectron Spectroscopy (XPS) and near-edge x-ray absorption fine structures (NEXAFS) spectroscopy

In the last few years, double-core-hole states (DCHs) have been extensively studied by single photon double-core ionization at synchrotron centers [1] and, in relation to X-ray two photon double-core spectroscopy [2], at X-ray free electron laser facilities (XFELs). Closely related to double core ionization, the single photon process where a core electron is ionized while another core electron is excited simultaneously, reveals interesting properties on the formation mechanisms of K⁻²V states and provides a new spectroscopic insight that offers the advantages of both XPS and NEXAFS spectroscopies.

The creation of K⁻²V states and their subsequent decay are the following:

$$hv + AB \rightarrow AB^{+}(K^{-2}V) + e^{-}_{ph} \rightarrow AB^{++} + e^{-}_{A1} \rightarrow AB^{3+} + e^{-}_{A2}.$$

Since one photoelectron and two Auger electrons are emitted, by detecting in coincidence these three electrons, it is possible to filter out the specific photoelectron spectrum associated with K⁻²V states. This can be done very efficiently by using a magnetic bottle time-of-flight electron spectrometer under single bunch operation at SOLEIL (France) and Photon Factory (Japan).

The study of the above process for the C₂H₂n (n=1-3) series [3] has revealed a NEXAFS signature in the spectra (Fig.1). Two competing channels appear with comparable intensities:

- The first one corresponds to the dipolar ionization of a core electron accompanied by monopolar excitation (direct shake-up) of the remaining core electron and can be interpreted as a “Super” K⁻<fnref n="1" /> satellite state.

- The second one corresponds to the dipolar excitation of a core electron to a vacant orbital accompanied by monopolar shake-off of the

other core electron (conjugate shake-up process) which has a NEXAFS-like character.

Close to the K⁻² threshold, these two processes appear with comparable intensities. This can be understood as resulting from aborted double-core ionization where one of the outgoing electrons is recaptured in a vacant orbital. At higher photon energy, the conjugate shake-up process is unfavorable since the sudden approximation leads only to the direct process.

<figure><img src="image_2.png" /><figcaption>**Figure 1:** Experimental and theoretical K⁻²V spectra in C₂H₂n series at a photon energy $hv = 770$eV.</figcaption></figure>

Examples on small molecules: H₂O [4], N₂ [5] and many others, have been obtained, which show how powerful this new spectroscopy is and allows also a better interpretation of resonances appearing in NEXAFS spectrum.

References

[1] Lablanquie et al 2011, Phys. Rev. Lett. **106**, 063003

[2] Santra et al 2009, Phys. Rev. Lett. **103**, 013002

[3] Nakano et al 2013, Phys. Rev. Lett. **111**, 123001

[4] Carniato et al 2015, J. Chem. Phys. **142**, 014307

[5] Carniato et al 2015, J. Chem. Phys. **142**, 014308

<footnote>* Sorbonne Université, UPMC and CNRS, LCP-MR (UMR 7614), 11 rue P. & M. Curie, 75231 Paris Cedex 05, France
& Jozef Stefan Institute, P.O. Box 3000, SI-1001 Ljubljana, Slovenia</footnote>

<footnote>£ UVSOR Facility, Institute for Molecular Science, Okazaki 444-8585, Japan</footnote>

<footnote>† Institute of Materials Structure Science, Photon Factory, Tsukuba, Ibaraki 305-0801, Japan</footnote>

<footnote># Department of Environmental Science, Niigata University, Niigata 950-2181, Japan</footnote>

<footnote n="1">¹ E-mail: francis.penet@upmc.fr</footnote>

<footnote>*² E-mail: stephane.carniato@upmc.fr</footnote>