# Étude par spectroscopie Auger de l'interaction post-collisionnelle d'ions solvatés ionisés en couche K

Bastien Lutet-Toti, Jérôme Palaudoux, Francis Penent, Pascal Lablanquie,

Sergei Sheinerman, Leonid Gerchikov, Thanit Saisopa, Yuttakarn

Rattanachai, Denis Céolin

<figure><img src="image_1.png" /></figure>

## ► To cite this version:

Bastien Lutet-Toti, Jérôme Palaudoux, Francis Penent, Pascal Lablanquie, Sergei Sheinerman, et al. "Étude par spectroscopie Auger de l'interaction post-collisionnelle d'ions solvatés ionisés en couche K. Journées Nationales des Spectroscopies de PhotoEmission (JNSPE), May 2022, Dijon, France." [hal-03967513]

HAL Id: hal-03967513

https://hal.science/hal-03967513

Submitted on 1 Feb 2023

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_2.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
## PCI of the KLL transition

* Inner-shell photoionization of the 1s orbital leads to the emission of a photoelectron and to the creation of a short-lived unstable $1s^{-1}$ state that can relax by emission of a subsequent Auger electron and leads to a final $2p^{-2}$ state.

* For a photon energy just above the 1s ionization threshold : a **strong coulombic interaction** between the Auger electron, the photoelectron and the ionic core exists.

* The photoelectron undergoes a fast change of the ionic charge ($+1 \rightarrow +2$) when the Auger electron overtakes it and is slowed down. Conversely, the Auger electron is accelerated when overtaking the photoelectron.

<figure><img src="image_3.png" /></figure>

Near threshold

Far above threshold

<figure><img src="image_4.png" /></figure>

Near threshold

Or

<figure><img src="image_5.png" /></figure>

Far above threshold

* Energy exchange between photoelectron and Auger electron.

* Leads to opposite shifts and distortions of the emitted photo- and Auger electrons peaks in the **vicinity of inner-shell ionization threshold**

* This effect is known as **post collision interaction (PCI)**.

$$ (M^{*+}(1s^{-1}) + e_{ph} \rightarrow M^{2+}(2p^{-2}) + e_{A} + e_{ph}) $$

## Screening effect and motivation

* In the **gas phase** and **tender X-ray** domain (1-5 keV), the PCI effect was studied on Argon [1]. A maximum shift (0.8 eV) of the main KLL Auger peak (¹D) is observed and decreases while increasing photon energy.

* In solid phase (surface and bulk), the energy shift could be also influenced by the modification of the effective charge of the residual ion [2]

* Hence, applied to the **aqueous phase**, we chose to study by Auger spectroscopy, the PCI effect on different **isoelectronic** ions to Argon : hydrated $Cl^{-}$, $K^{+}$, $Ca^{2+}$.

## Experimental Set-Up

* Experiments were conducted at the GALAXIES [3] beamline (2.3 – 12 keV) of the SOLEIL synchrotron (France) with a **liquid micro-jet** [4] adapted for the **HAXPES** [5] photoemission end-station.

<figure><img src="image_6.png" /><figcaption>Drawing of the principle of a hemispherical analyzer</figcaption></figure>

Picture took @ GALAXIES in December 2020

* HAXPES resolution : 375 meV

* KCl and $CaCl_2$ solutions were prepared at 0.5 M in water

* Degassing and filtering of the solutions were systematically performed

## Experimental results in water

* To evaluate the PCI shift, we focused our study onto the $2p^{-2}$ (¹D) peak (the most intense and well isolated) as a function of the photon energy.

* We calibrated the photon energy.

* We defined the Excess Energy (EE) : photon energy minus the **ionization potential** of the ion targeted : $EE = hv - IP$ ; the Energy Shift (ES) : shift of the Auger ¹D peak recorded close to the threshold relative to the position of the same peak recorded far above the threshold : $ES = E_k (¹D) - E_k (¹D)$ (unshifted)

* **Van der Straten** calculations type were performed by our colleagues S. Sheinerman and L. Gerchikov [6]

$$ ES = \frac{\Gamma_{tot} \cdot C}{2} \times \frac{e^2}{\hbar} \quad \text{with:} \quad C = \frac{1}{\epsilon} \left( \frac{1}{v_{ph}} - \frac{1}{|v_A - v_{ph}|} \right) $$

* The total width depends on the ionic autoionization width $\Gamma_a$ and the photoelectron **damping term** $\Gamma_d$ in the water. This later is expressed as a function of the velocity of the photoelectron and of the **electron mean free path**, $l$

$$ \Gamma_{tot} = \Gamma_{a} + \Gamma_{d} = \Gamma_{a} + \frac{\hbar v_{ph}}{l} \quad \text{With:} \quad v_{ph} = \sqrt{2EE/m} $$

## KLL Auger spectra

<figure><img src="image_7.png" /></figure>

## Shift of the ¹D peak vs VDS

<figure><img src="image_8.png" /></figure>

## PCI shift in water

* A decrease of the PCI effect **slower** than the argon case ( due to screening effect and to the reduced mean free path)

* Shift just above threshold **greater** for ions than for Ar (1 eV versus 0.8 eV)

* A **charge/size effect**

<figure><img src="image_9.png" /><figcaption>PCI shift the ¹D KLL peaks for the ions $Cl^{-}$, $K^{+}$ and $Ca^{2+}$ in water in comparison with the results obtained for Ar in the vicinity of the 1s ionization thresholds of each studied ion.</figcaption></figure>

## Conclusions and perspectives

* Our study shows a **PCI effect** in the KLL Auger decay of several ions isoelectronic to argon, studied in aqueous phase. The position of the ¹D peak maximum in the Auger spectra shows a shift of a value larger than the one observed on gas phase Argon. The PCI shift in the aqueous case decreases slowly with photon energy.

* An initial **charge effect** is observed.

* A solvent effect is observed

* Theoretical investigations of the PCI effect show that the model depends on an additional term linked to the mean free path of the medium.

## References

[1] R. Guillemin et al., Phys.Rev A, **92**, 012503 (2015)

[2] T. Miller and T.-C. Chiang, Phys Rev B, **29**, 1121-1124, (1994)

[3] J.-P. Rueff et al., J. Synch.Rad, **22**, 175-179 (2015)

[4] D. Ceolin et al., PhysRev Lett **119**, 263003 (2017)

[5] J.-P Rueff et al., J. Synch.Rad, **31**, 4-9, (2018)

[6] P. van der Straten et al., Z.Phys.D-Atoms,Molecules and Clusters, **8**, 35-45,(1988)

[7] G. M. Hale and M. R Querry, Applied Optics **12**, 3 (1973)

[8] Y-I.Suzuki et al., PRE **90**, 010302 (R) (2014)