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We developed recently [A. Fert\'e, et al., J. Phys. Chem. Lett. 11, 4359 (2020)] a method to compute single site double core hole (ssDCH or K$^{-2}$) spectra. We refer to that method as NOTA+CIPSI. In the present paper this method is applied to the O K$^{-2}$ spectrum of the CO$_2$ molecule, and we use this as an example to discuss in detail its convergence properties. Using this approach, a theoretical spectra in excellent agreement with the experimental one is obtained. Thanks to a thorough interpretation of the shake-up states responsible for the main satellite peaks and with the help of a comparison with the O K$^{-2}$ spectrum of CO, we can highlight the clear signature of the two non equivalent carbon oxygen bonds in the oxygen ssDCH CO$_2$ dication., Comment: 16 pages, 7 figures, 7 tables

We recently developed [A. Ferté

The Auger decay process of the $3{d}_{5/2}$ hole is studied experimentally and theoretically along the isoelectronic Br, ${\mathrm{Kr}}^{+}$, and ${\mathrm{Rb}}^{2+}$ series with electron configuration [Ar] $3{d}^{9}4{s}^{2}4{p}^{6}$. The experimental results consist of multielectron coincidence data measured from all three elements and conventional high-resolution Auger spectrum for the Br case. Theoretical interpretation was done by using multiconfiguration Dirac-Fock calculations. It is found that the decay rate of two-Auger-electron emission increases along the series in the direction of decreasing nuclear charge. Also, complexity of the Auger spectrum follows the same trend, requiring a drastic increase to the size of the configuration space for describing the observed spectra.

International audience; Double core hole spectroscopy is an ideal framework for investigating photoionization shake-up satellites. Their important intensity in a single site double core hole (ssDCH) spectrum allows the exploration of the subtle mix of relaxation and correlation effects associated with the inherent multielectronic character of the shake-up process. We present a high accuracy computation method for single photon double core shell photoelectron spectra that combines a selected configuration interaction procedure with the use of non orthogonal molecular orbitals to obtain unbiased bindingenergy and intensity. This strategy leads to oxygen ssDCH spectrum of the CO molecule that is in excellent agreement with the experimental result. Through a combined wave function and density analysis, we highlight that the most intense shake-up satellites are characterized by an electronicreorganization that opposes the core hole induced relaxation.

Multi-electron coincidence spectroscopy using a magnetic-bottle electron spectrometer has been applied to the study of the Auger decay following O1s photoionization of condensed H 2 O molecules. Coincidence Auger spectra are obtained for three different photoelectron energy ranges. In addition, the energy distribution of the slow electrons ejected in the Auger decay of the O1s core hole is deduced from three-fold coincidences.

Single photon simultaneous core ionization/core excitation (K−2V) of the Benzene molecule has been observed experimentally, using synchrotron radiation, by electron coincidence spectroscopy with a magnetic bottle time-of-flight electron spectrometer and reveals a rich spectrum. DFT and Post–Hartree–Fock calculations provide detailed assignments of K−2V states. The specific Auger decay of these states has also been determined experimentally with a new technique to improve the energy resolution.

We have studied single photon double K-shell ionization of small molecules (N2, CO, C2H2n (n = 1–3), …) and the Auger decay of the resulting double core hole (DCH) molecular ions thanks to multi-electron coincidence spectroscopy using a magnetic bottle time-of-flight spectrometer. The relative cross-sections for single-site (K−2) and two-site (K−1K−1) double K-shell ionization with respect to single K-shell (K−1) ionization have been measured that gives important information on the mechanisms of single photon double ionization. The spectroscopy of two-site (K−1K−1) DCH states in the C2H2n (n = 1–3) series shows important chemical shifts due to a strong dependence on the C C bond length. In addition, the complete cascade Auger decay following single site (K−2) ionization has been obtained.

Ultrafast dissociation of the HCl and HBr molecules excited respectively to the 2p 3/2 → σ* and 3d 5/2 → σ* resonances are studied with high resolution photoelectron spectroscopy. Sharp vibrational molecular lines and broad atomic lines are observed. The analysis of the profile of the atomic lines gives access to the lifetimes of the inner shell 2p 3/2 hole in the Cl* (2p 3/2 ) −1 3s 2 3p 6 configuration, and the inner shell 3d 5/2 hole in the Br* (3d 5/2 ) −1 4s 2 4p 6 configuration.

An Auger-electron–ion coincidence method is applied to study the site-specific formation of metastable CO 2 2+ in the C1s and O1s Auger decays of CO 2 . It is found that only dication states with the electronic configuration of 1π g −2 are relevant to the metastable formation. These dication states are favorably produced in the O1s Auger decay, because of the charge distribution of the 1π g orbital localizing at the O site. Fragmentation channels of dissociative CO 2 2+ states are also investigated.

The energy resolution and the detection efficiency of a magnetic bottle electron spectrometer equipped with an electrostatic retarder are examined, with a particular focus on its application to electron coincidence measurements. The electrostatic retardation properly improves the energy resolving power of the spectrometer. No significant decrease in detection efficiency is observed when retardation voltages are applied. Photoelectron–Auger electron coincidence measurement of the L2,3VV Auger decay in CS2 is performed by using the magnetic bottle spectrometer, which reveals Auger transition intensities varying for the different core holes.

International audience; In the last five years, a strong experimental and theoretical activity has been dedicated to the study of inner-shell double photoionization. Almost simultaneously, between 2009 and 2011, different experiments were performed using two different light sources: well established third generation synchrotron light sources that exist for more than two decades and recently developed x-ray free electron lasers (X-FEL) that provide brightness about 10 orders of magnitude higher. The high photon flux of X-FEL has made possible the successive absorption of many x-ray photons by inner-shell electrons in femtosecond timescale. The possibility to create multiple inner-shell vacancies with this new X-FEL light source has resuscitated “prophetic” 25 years old calculations by Cederbaum et al. [1][2] concerning double K-shell ionization that could be of great interest when conventional Electron Spectroscopy for Chemical Analysis (ESCA) finds some limitations. As a feedback, this has stimulated new theoretical developments. On the other hand, it was considered practically out of reach to observe such states with conventional third generation synchrotron light sources due to the very weak probability to eject two inner-shell electrons by a single photon when the dominant process, that could mask everything else, is single inner-shell ionization. However, due to the development of very efficient detection techniques, it was also possible to perform spectroscopy of double core-hole states with excellent accuracy using third generation synchrotron sources.In this paper we give an outlook, on the basis of recently published results, of the complementary of these light sources for double core-hole spectroscopy. Some new developments and results are also presented with a prospective of what could be done in the future with the technical breakthrough that will be necessary to improve further our understanding of chemical analysis.

We have measured vibrationally-resolved molecular-frame photoelectron angular distributions (MF-PAD) from the C 1s level of CO molecules in the σ shape resonance region. The MF-PAD’s for vibrational levels ( v f =0, 1, and 2) in the C 1s→ e lσ channel are apparently different one from another at each incident photon energy. These experimental MF-PAD’s agree with the present theoretical results from averaging the nuclear distance dependent dipole matrix elements with the relaxed core Hartree–Fock calculations. The results show that the MF-PAD’s sensitively depend on the vibrational levels. This means that the internuclear distance dependences of phases and of magnitudes of dipole matrix elements play a crucial role in the C 1s photoionization of CO.

Differential cross sections have been measured for vibrationally elastic scattering of electrons from ozone molecules at incident electron energies from 2 eV to 10 eV in the angular range from 20° ...

Angular distributions of C 1s photoelectrons from fixed-in-space CO molecules have been measured with vibrational resolution. A strong dependence of the angular distributions on the vibrational states of the residual molecular ion has been found for the first time in the region of the shape resonance. Calculations in the relaxed core Hartree-Fock approximation have reproduced the angular distributions fairly well in the general shapes of the angular distributions due to the correct description of nuclear motion as an average of the internuclear-distance-dependent dipole amplitudes.

Angular distributions of photoelectrons (ADPs) from the 2σg shell of a fixed-in-space N2 molecule have been measured for left- and right-elliptically polarized, as well as for linearly polarized, light. From these data a set of dipole matrix elements and phase shift differences characterizing the process has been determined taking into account the acceptance angles of both electron and ion detectors, i.e. the complete experiment has been performed. Good agreement between the experimental and the relevant theoretical values calculated in the random phase approximation is obtained. Based on the results of the complete experiment, three-dimensional ADPs and ions are predicted for different light polarizations.

Angular distributions of photoelectrons from both C and O K-shells of the fixed-in-space CO molecule have been measured using the angle-resolved photoelectron-photoion coincidence technique. The measurements have been performed at several photon energies from the ionization thresholds up to about 30 eV above them, where the σ* shape resonances occur. Experimental results are compared with the multiple-scattering calculations of Dill et al (1976 J. Chem. Phys. 65 3158) and with our new calculations in the relaxed-core Hartree-Fock approximation. Our calculations are in a better agreement with the experimental data though numerical discrepancies remain. The experimental angular distributions are fitted by the expansion in Legendre polynomials containing up to ten terms and the extracted parameters are compared with the corresponding theoretical values.

Using the experimental angular distributions of photoelectrons from the K-shells of an oriented CO molecule reported in a companion paper, we have performed a so-called complete experiment and determined 18 dynamical parameters (ten moduli of transition moments and eight phase differences) for the O K-shell, and 16 dynamical parameters (nine moduli of transition moments and seven phase differences) for the C K-shell, and compared them with the results of our calculations in the relaxed-core Hartree-Fock (RCHF) approximation. The agreement between theory and experiment is only qualitative, therefore the model has to be improved by including electron correlations. From the analysis of experimental data we proved that the σ* shape resonance is due to not only the f-wave, as was widely believed earlier, but is due to approximately equal contributions of three partial waves with 1≤l≤3 for the C K-shell, and four partial waves with 0≤l≤3 for the O K-shell, with a rather substantial contribution of other partial waves with l≤5. From the analysis of the transition moments determined from the experiment it follows that several Cooper minima are likely to exist in partial photoionization cross sections, in particular, in the C 1sσ→esσ and in the O 1sσ→edσ transitions.

The angular distribution of photoelectrons from fixed-in-space molecular hydrogen has been measured in the 44-76 eV photon energy range for an ionic state, with a state energy of 38 eV measured from the H2 ground state, dissociating to H+ +H(n = 2). The photoelectrons are ejected nearly isotropically at 44 eV when their energy is relatively low, while ejection perpendicular to the molecular axis becomes more and more favoured as the photon energy increases. This behaviour is possibly explained in terms of direct photoionization to the 2p u and 2s g states of H2 + ; the former being favoured at 44 eV, and the latter at photon energies far from threshold.

The first complete experiment for the C $K$-shell of CO molecules in the region of the ${\ensuremath{\sigma}}^{*}$ shape resonance has been performed by detecting photoelectrons in coincidence with fragment ions. Four ratios of dipole matrix elements and four phase shift differences have been extracted from the experimental data. Their analyses show that, in the ${\ensuremath{\sigma}}^{*}$ shape resonance due to the $l$ mixing, $d$ and $f$ partial waves give the main contribution to the cross section, and $f$ and $g$ waves give the main contribution to a rapid increase of phase shift by $\ensuremath{\pi}$.

Angular distributions of $1s{\ensuremath{\sigma}}_{g,u}$ photoelectrons from C${\mathrm{O}}_{2}$ molecules, oriented parallel to the electric vector of incident light, have been measured. The angular distribution patters at ${\ensuremath{\sigma}}_{g}^{*}$ and ${\ensuremath{\sigma}}_{u}^{*}$ shape resonances are significantly different from those expected in the virtual molecular orbitals concept. The analyses of the patterns have made it clear that the mixing of outgoing photoelectron partial waves and the interference between them are responsible for the observed patterns, unlike ${\mathrm{N}}_{2}$ photoionization. Calculations based on a quasiatomic model have reproduced the observed patterns fairly well.

The status of cross section measurements carried out with a Mini-EBIS- is reported, here. Single- and multiple-electron transfer processes in collisions of Arq+ (q = 6, 7, 8, 9, and 11) with H2 and He, and those of C4+ with Ne, Ar and Kr have been investigated at low energies ranging from 0.075 eV/amu to 275 eV/amu and from 0.33 eV/amu to 667 eV/amu, respectively. All data of single-electron transfer cross sections measured for Arq+ −H2 and −He systems shows a similar tendency to converge toward the Langevin cross section at the low energy end. In the C4+ −Ne system, double-electron transfer is predominant at high energies and it is dominated by the backward scattering at low energies. From the observation of recoil ions produced in C4+ −Ar and −Kr collisions, it is found that the angular distribution of the multiple-electron transfer collisions shifts toward the backward direction in the center-of-mass frame with decreasing collision energy and four-electron transfer processes take place. The importance of the orbiting effect due to the polarization force and the backward scattering are enhanced in the single- and multiple-electron transfer collisions of highly charged ions at low energies.

We have observed single photon double $K$-shell photoionization in the ${\mathrm{C}}_{2}{\mathrm{H}}_{2n}$ ($n=1--3$) hydrocarbon sequence and in ${\mathrm{N}}_{2}$ and CO, using synchrotron radiation and electron coincidence spectroscopy. Our previous observations of the ${K}^{\ensuremath{-}2}$ process in these molecules are extended by the observations of a single photon double photoionization with one core hole created at each of the two neighboring atoms in the molecule (${K}^{\ensuremath{-}1}{K}^{\ensuremath{-}1}$ process). In the ${\mathrm{C}}_{2}{\mathrm{H}}_{2n}$ sequence, the spectroscopy of ${K}^{\ensuremath{-}1}{K}^{\ensuremath{-}1}$ states is much more sensitive to the bond length than conventional electron spectroscopy for chemical analysis spectroscopy based on single $K$-shell ionization. The cross section variation for single photon ${K}^{\ensuremath{-}1}{K}^{\ensuremath{-}1}$ double core ionization in the ${\mathrm{C}}_{2}{\mathrm{H}}_{2n}$ sequence and in the isoelectronic ${\mathrm{C}}_{2}{\mathrm{H}}_{2}$, ${\mathrm{N}}_{2}$ and CO molecules validates a knock-out mechanism in which a primary ionized $1s$ photoelectron ejects another $1s$ electron of the neighbor atom. The specific Auger decay from such states is clearly observed in the CO case.

The angular correlation between photo- and Auger electrons in xenon has been measured for right and left circularly polarized light with 110 eV energy. Thanks to the high degree of circular polarization of the helical undulator radiation, the circular dichroism in the angular correlation has been clearly observed.

The cross sections for single-electron capture, including transfer ionization, and for double-electron capture, have been measured for Ar{sup {ital q}+}+H{sub 2} for {ital q}=6, 7, 8, 9, and 11 with projectile energies from {ital q} eV to {ital q} keV. Theoretically, the cross sections for Ar{sup 6+} and Ar{sup 8+} impact were calculated using a molecular-orbital expansion method in the energy region from 240 eV to 80 keV, and are in good agreement with experiment. The single-electron-capture cross sections were found to be more than one order of magnitude larger than those for double capture in both experiment and theory. The single-electron-capture cross sections were also compared to the Langevin cross section, a scaling law developed by Mueller and Salzborn [Phys. Lett. 62A, 391 (1977)], and the absorbing sphere model.

Double Auger decay of O1s(-1) and its satellite states in H(2)O has been studied with a multi-electron coincidence method, and a process leading to autoionizing O* fragments has been revealed. The breaking of the two O-H bonds producing the autoionizing O* fragments occurs for highly excited H(2)O(2+) populated by the initial Auger decay. The O* fragments are more favorably produced in the decay from the satellite states, resulting from the larger population of highly excited H(2)O(2+) states inheriting the valence excitation in the initial state.

The Auger decay channels of the Ar 2$p$ satellite states have been investigated using a multielectron coincidence technique, using a magnetic bottle time-of-flight electron spectrometer. For the Ar${}^{+}$(2${p}^{\ensuremath{-}1}$3${p}^{\ensuremath{-}1}np$) satellite states the 2$p$ hole is filled first, while for the Ar${}^{+}$(2${p}^{\ensuremath{-}1}$3${s}^{\ensuremath{-}1}$4$s$) satellite states the 3$s$ hole is filled first with leading to Ar${}^{2+}$(2${p}^{\ensuremath{-}1}$3${p}^{\ensuremath{-}1}$) states, which subsequently undergo an Auger decay leading to the filling of the 2$p$ hole.

We observe the formation in a single-photon transition of two core holes, each at a different carbon atom of the C2H2 molecule. At a photon energy of 770.5 eV, the probability of this 2-site core double ionization amounts to 1.6 ± 0.4% of the 1-site core double ionization. A simple theoretical model based on the knockout mechanism gives reasonable agreement with experiment. Spectroscopy and Auger decays of the associated double core hole states are also investigated.

The direct observation of triple photoionization involving one inner shell and two valence electrons is reported. The energy distribution of the three photoelectrons emitted from Ne is obtained using a very efficient multielectron coincidence method using the magnetic bottle electron spectroscopic technique. A predominance of the direct path to triple photoionization for the formation of Ne3+ in the 1s 2s2 2p4 configuration is observed. It is demonstrated that the energy distribution evolves with photon energy and indicates a significant difference with triple photoionization involving only valence electrons.

The formation of hollow molecules (with a completely empty K shell in one constituent atom) through single-photon core double ionization has been demonstrated using a sensitive magnetic bottle experimental technique combined with synchrotron radiation. Detailed properties are presented such as the spectroscopy, formation, and decay dynamics of the N(2)(2+) K(-2) main and satellite states and the strong chemical shifts of double K holes on an oxygen atom in CO, CO2, and O2 molecules.

Cross sections for single and multiple electron capture in collisions of C4+ with H2, N2 and O2 have been measured within the energy range 0.33-666 eV amu-1. Where comparison is possible, the results are in good agreement with previous measurements at higher energies. Below 100 eV amu-1 there are significant differences between experiment and the currently available theories.

The total attenuation cross section sigma att and the single-electron capture cross section sigma 21 in collisions of 3He2+ with H2 have been measured using a tandem mass spectrometer whose collision cell consists of an octopole ion beam guide. A possible scattering loss which might contribute to sigma att is examined, and a large part of the difference sigma att- sigma 21 is attributed to the double-electron capture process. As its magnitude is as large as 10-15 cm2 at the lowest energy studied. The importance of the process is emphasized in connection with the production of fast protons through Coulomb explosion of H2+2.

A small size electron beam ion source (mini-EBIS) cooled with liquid nitrogen has been developed for atomic collision research. An experimental technique using mini-EBIS in combination with an octupole ion beam guide (OPIG) has proved very useful for low energy collision experiments including highly charged ions. Single and double electron capture cross sections in collision systems of C4+He, N4+He and O4+ have been measured at low energies from 0.5 to 2000 eV in the center of mass system.

We have studied the site-specific formation of metastable OCS2+ in the C1s and the O1s Auger decays of OCS molecules by using an Auger-electron–ion coincidence technique. The coincidence measurement reveals the metastable character of the Auger final states with the (3π)−2 configuration. The formation of metastable OCS2+ is observed negligibly in the C1s Auger decay and only weakly in the O1s Auger decay, in contrast to the favorable metastable formation previously reported for S2p Auger decay. It is found that the origin of the site-specificity in the formation of metastable OCS2+ arises from the localization effect of the valence orbital involved in the Auger transition. The dissociative dication states related to individual fragmentation pathways are also derived from the coincidence measurement.

Helium double photoionization (γ,2e) triple differential cross sections (TDCSs) were measured at an excess energy of 60 eV using a dual toroidal spectrometer and synchrotron radiation from a helical undulator (BL-28A, Photon Factory, Japan). Energy-sharing ratios (R=E 2 /E 1 ) for the two ejected electrons of 5 and 11 are studied with both right- and left-handed elliptically polarized light. The TDCSs are found to be in good agreement with those obtained using the hyperspherical R matrix with semiclassical outgoing waves theory. The circular dichroism for a limited mutual angular range (Φ 1 2 110°-200°) is determined from the experimental data for both R= 5 and 11, and compared to theoretical calculations performed over the complete range of mutual angles. No dynamic nodes are found in either the experimental (within the explored Φ 1 2 range) or theoretical circular dichroism for these R values at this excess energy.

Angular distributions of photoelectrons from a 2sigma(g) shell of fixed-in-space N2 molecules have been measured for left- and right-elliptically polarized and for linearly polarized light at several photon energies in the region of sigma(*) shape resonance. That allowed the determination of a set of dipole matrix elements and phase shift differences characterizing the process. These data clearly show the enhancement of the fsigma(u) partial cross section in the resonance simultaneously with an abrupt increase of the corresponding phase shift by pi, which is the first experimental demonstration of the nature of the sigma(*) shape resonance in homonuclear diatomic molecules.

Triple differential cross sections (TDCSs) of the two ejected chiral electrons from helium were measured for several kinematic conditions using circularly polarized synchrotron radiation at the Photon Factory. The selected kinematic conditions were E=9 eV (R=2,8), E=40 eV (R=7,19) and E=50 eV (R=24), where E is the excess energy and R is the ratio of the kinetic energy of the ejected electrons. The changes in the TDCSs with “E” and “R” are presented. The gerade (ag) and ungerade (au) dipole amplitudes were determined using four parameters parametrization. The “E” and “R” dependences of the four parameters of ag and au are also presented.

We have observed single photon one-site (K?2) and two-sites (K?1K?1) double K-shell ionization in C2H2n (n=1-3) sequence and in isoelectronic C2H2, N2 and CO molecules. The spectroscopy of K?1K?1 states is much more sensitive to the bond length than conventional ESCA spectroscopy based on single K-shell ionization. The mechanism of single photon two-sites is due to a knock-out process in which a primary photoionized 1s electrons eject another 1s electron on the neighbor atom.

The breakup of D 2 following the absorption of a single photon, leading to four free charged particles interacting via the Coulomb force, has been investigated. Triply differential cross sections (TDCSs) of the two ejected electrons were measured for selected asymmetric kinematic conditions, namely, a 20 eV electron in coincidence with a 5 eV "reference" electron fixed at four different angles. The results are compared with helium TDCSs and, although the respective angular distributions have similar features, there are surprising differences that could have their origin in two-center interference effects.

Angular correlation patterns of N5-O23O23 1S0 Auger electrons in coincidence with 4d5/2 photoelectrons in two-step double photoionization of xenon and those of two emitted photoelectrons in coincidence with each other in direct double photoionization of helium have been studied with elliptically polarized photons. Circular dichroism in the angular distribution patterns has been reported in both cases.

The dynamical information (ten dipole matrix elements and eight phase differences) has been deduced from the measured angular distributions of photoelectrons from O $K$ shell of oriented CO molecules near the ionization threshold in the region of a ${\ensuremath{\sigma}}^{*}$ shape resonance. Light polarization parallel and perpendicular to the molecular axis has been used. An important contribution of six $l\ensuremath{\sigma}$ partial waves with $0\ensuremath{\le}l\ensuremath{\le}5$ to the ${\ensuremath{\sigma}}^{*}$ shape resonance is demonstrated. A comparison with our calculations in the relaxed core Hartree-Fock approximation reveals only a qualitative agreement, therefore a more advanced theory is needed.

Electron reemission following photoelectron recapture due to post-collision interaction has been studied at 0.7 eV the inner-shell photoionization threshold of water molecules, using a multi-electron coincidence method. Electron reemissions after single Auger decay occur from O and OH fragments which are produced by the dissociations of high-n Rydberg H2O(+) states populated through photoelectron recapture. In addition, electron reemissions after double Auger decay are identified in triple coincidence events, where autoionization lines from O and O(+) fragments are observed.

The cross sections for single‐ and double‐electron transfer, neglecting the transfer ionization processes, have been measured for Arq+ (q=6, 7, 8, 9 and 11) with H2 and He at low energies ranging from 0.075 to 225 eV/amu, systematically. The single‐electron transfer cross sections were found to distribute between the predictions of the scaling law by Muller and Salzborn and the absorbing model by Olson and Salop above about 1 eV/amu and to converge to the Langevin cross section at the low energy end measured. For the same projectile ion, the single‐electron transfer cross sections for the H2 targets are about threefold as large as those for the He target and both energy dependencies are very similar. The double‐electron transfer cross sections are smaller than those for the single‐electron transfer and they are characterized by a minimum structure near 1 eV/amu for He targets. All cross sections for the single‐ and double‐electron transfer have a common signature increasing with decreasing collision energ...

Single photon double K-shell ionization of small molecules (N2, O2, CO, CO2) has been observed by coincidence detection of two photoelectrons with two Auger electron and reveals properties of hollow molecules.

Cascade Auger electron emission following Xe 3d photoionization has been investigated using a multi-electron coincidence technique, which utilizes an electron spectrometer of magnetic bottle type. It has been found that the Xe2+ states of the 4p−14d−1 configuration, formed by the Auger decay of the Xe+ 3d3/2, 5/2−1 states, dominantly turn into triply charged states of the 4d−25p−1/4d−25s−1 configurations. The Xe2+ 4s−14d−1 states, formed by the 3d Auger decay, yield the 4p−14d−15p−1 states as well as the 4d−3 states. From the coincidence spectrum among three Auger electrons, it is suggested that the Xe2+ 4p−14d−1 states give rise to the following cascade processes: 4p−14d−1 → 4d−25p−1 → 4d−15p−3.

The cross‐sections for single and double charge exchange have been measured for Arq++H2 for q=6, 7 and 8. The single charge exchange cross‐section can be modeled by a combination of the Langevin cross‐section for the low energy region and the Muller and Salzborn scaling law for the higher energies. Good agreement was found for charge states 6 and 7, for 8 the experimental data was slightly lower.