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Sökning: WFRF:(Céolin D.)

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1.
  • Ankowski, A., et al. (författare)
  • Energy reconstruction of electromagnetic showers from Ν0 decays with the ICARUS T600 liquid argon TPC
  • 2010
  • Ingår i: Acta Physica Polonica, Series B.. - 1509-5770 .- 0587-4254. ; 41:1, s. 103-125
  • Tidskriftsartikel (refereegranskat)abstract
    • We discuss the ICARUS T600 detector capabilities in electromagnetic shower reconstruction through the analysis of a sample of 212 events, coming from the 2001 Pavia surface test run, of hadronic interactions leading to the production of π 0 mesons. Methods of shower energy and shower direction measurements were developed and the invariant mass of the photon pairs was reconstructed. The (γγ) invariant mass was found to be consistent with the value of the π 0 mass. The resolution of the reconstructed π 0 mass was found to be equal to 27.3%. An improved analysis, carried out in order to clean the full event sample from the events measured in the crowded environment, mostly due to the trigger conditions, gave a π 0 mass resolution of 16.1%, significantly better than the one evaluated for the full event sample. The trigger requirement of the coincidence of at least four photo-multiplier signals favored the selection of events with a strong pile up of cosmic ray tracks and interactions. Hence a number of candidate π 0 events were heavily contaminated by other tracks and had to be rejected. Monte Carlo simulations of events with π 0 production in hadronic and neutrino interactions confirmed the validity of the shower energy and shower direction reconstruction methods applied to the real data.
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2.
  • Ankowski, A, et al. (författare)
  • Energy reconstruction of electromagnetic showers from π0 decays with the ICARUS T600 liquid argon TPC
  • 2010
  • Ingår i: Acta Physica Polonica B. - : Jagellonian University. - 0587-4254 .- 1509-5770. ; 41:1, s. 103-125
  • Tidskriftsartikel (refereegranskat)abstract
    • We discuss the ICARUS T600 detector capabilities in electromagnetic shower reconstruction through the analysis of a sample of 212 events, coming from the 2001 Pavia surface test run, of hadronic interactions leading to the production of π0 mesons. Methods of shower energy and shower direction measurements were developed and the invariant mass of the photon pairs was reconstructed. The (γ,γ) invariant mass was found to be consistent with the value of the π0 mass. The resolution of the reconstructed π0 mass was found to be equal to 27.3%. An improved analysis, carried out in order to clean the full event sample from the events measured in the crowded environment, mostly due to the trigger conditions, gave a π0 mass resolution of 16.1%, significantly better than the one evaluated for the full event sample. The trigger requirement of the coincidence of at least four photo-multiplier signals favored the selection of events with a strong pile up of cosmic ray tracks and interactions. Hence a number of candidate π0 events were heavily contaminated by other tracks and had to be rejected. Monte Carlo simulations of events with π0 production in hadronic and neutrino interactions confirmed the validity of the shower energy and shower direction reconstruction methods applied to the real data.
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3.
  • Kukk, E., et al. (författare)
  • Photoelectron recoil in CO in the x-ray region up to 7 keV
  • 2017
  • Ingår i: PHYSICAL REVIEW A. - 2469-9926. ; 95:4
  • Tidskriftsartikel (refereegranskat)abstract
    • Carbon 1s photoelectron spectra of CO molecules in gas phase were recorded in the tender x-ray energy range, from 2.3 to 6.9 keV. The intensity ratios of individual peaks from nu = 0 to 3 within the vibrational progression of the C 1s photoelectron spectrum were determined at the various photon energies and are shown to be strongly affected by the photoelectron recoil effect. The experimental vibrational intensity ratios are compared with theoretical predictions at different levels of accuracy. Developments of the recoil model, using generalized Franck-Condon factors, rovibrational coupling, Morse potential energy curves, and accurate angular averaging are presented and applied to the analysis of the experimental results.
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4.
  • Li, S., et al. (författare)
  • Manifestation of postcollision interaction in Krypton LMN Auger spectra following K-shell photoionization
  • 2022
  • Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : American Physical Society. - 2469-9926 .- 2469-9934. ; 106:2
  • Tidskriftsartikel (refereegranskat)abstract
    • We report on an experimental and theoretical study of postcollision interaction (PCI) effects on L-2 - M4,5N2,3 Auger electrons measured above the Kr K-edge in which L-2 vacancies are primarily generated by KL2 x-ray emission. Such cascade processes, in which a deep inner-shell vacancy decays first by x-ray emission followed by Auger electron emission, is a strong decay mode in heavy atoms. The L-2 - M4,5N2,3 Auger electron peak is observed to become increasingly asymmetric with a shifting peak maximum as the absorbed x-ray energy approaches the K-shell ionization threshold. This is attributed to PCI energy exchanges of the Auger electron with the 1s photoelectron. To model the PCI effects, we have applied a semiclassical approach modified to account for the combined lifetimes of the K and L-2 hole states. In addition, our analysis treats several closely spaced Auger transitions with final ionic states having different terms and angular momenta.
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5.
  • Rubbia, C, et al. (författare)
  • Underground operation of the ICARUS T600 LAr-TPC : first results
  • 2011
  • Ingår i: Journal of Instrumentation. ; 6:07
  • Tidskriftsartikel (refereegranskat)abstract
    • Important open questions are still present in fundamental Physics and Cosmology, like the nature of Dark Matter, the matter-antimatter asymmetry and the validity of the Standard Model of particle interactions. Addressing these questions requires a new generation of massive particle detectors to explore the subatomic and astrophysical worlds. ICARUS T600 is the first large mass (760 tons) example of a new generation of detectors able to combine the imaging capabilities of the old famous “bubble chamber” with the excellent energy measurement of huge electronic detectors. ICARUS T600 now operates at the Gran Sasso underground laboratory and is used to study cosmic rays, neutrino oscillations and the proton decay. The potential for doing physics of this novel telescope is presented through a few examples of neutrino interactions reconstructed with unprecedented detail. Detector design and early operation are also reported.
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6.
  • Céolin, D, et al. (författare)
  • Partial ion yield spectroscopy around the Cl 2p and C 1s ionization thresholds in CF3Cl
  • 2009
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 131:24, s. 244301-
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a partial ion yield experiment on freon 13, CF3Cl, excited in the vicinity of the C 1s and Cl 2p ionization thresholds. We have collected a large amount of cationic fragments and a few anionic fragments at both edges. We have observed a strong intensity dependence of Rydberg transitions with ion fragment size for the CFnCl+ and CFn+/F+ (n=0-3) series at both the Cl 2p and C 1s ionization edges. Selectivity in the fragmentation processes involving the C-Cl and C-F bonds are highlighted by the intensities of the C 1s to lowest unoccupied molecular orbital (LUMO) and LUMO+1 transitions measured on the CFnCl+ and CFn+ yields. Equally, by comparison with their cation counterpart, we discuss possible bond-length dependence for the anion formation at the carbon 1s edge.
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7.
  • Feifel, Raimund, et al. (författare)
  • Cationic double K-hole pre-edge states of CS2 and SF6
  • 2017
  • Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 7
  • Tidskriftsartikel (refereegranskat)abstract
    • Recent advances in X-ray instrumentation have made it possible to measure the spectra of an essentially unexplored class of electronic states associated with double inner-shell vacancies. Using the technique of single electron spectroscopy, spectra of states in CS2 and SF6 with a double hole in the K-shell and one electron exited to a normally unoccupied orbital have been obtained. The spectra are interpreted with the aid of a high-level theoretical model giving excellent agreement with the experiment. The results shed new light on the important distinction between direct and conjugate shake-up in a molecular context. In particular, systematic similarities and di erences between pre-edge states near single core holes investigated in X-ray absorption spectra and the corresponding states near double core holes studied here are brought out.
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8.
  • Kosugi, S., et al. (författare)
  • Postcollision-interaction effects in multistep Auger transitions following Ar 1s photoionization
  • 2022
  • Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : American Physical Society. - 2469-9926 .- 2469-9934. ; 106:3
  • Tidskriftsartikel (refereegranskat)abstract
    • Postcollision-interaction (PCI) effects involving multistep decay processes following Ar 1s photoionization has been studied by Auger electron spectroscopy. The experiment focused on LMM Auger electrons measured in small photon energy steps across the Ar 1s photoionization threshold. Decay pathways that we studied include (1) the Ar+*2p-1 -> Ar2+3p-2 LMM alpha Auger process due to a single L hole created by KL fluorescence, (2) the Ar2+*2p-2 -> Ar3+*2p-13p-2 LMM1 Auger process following double L shell hole states produced by a KLL Auger processes, and (3) the subsequent Ar3+*2p-13p-2 -> Ar4+3p-4 LMM2 Auger transitions. Particularly pronounced PCI shifts and unusual line shapes compared to the ordinary one-step PCI process were found in the spectra of Auger processes following a KLL Auger first step. The experimental results were compared with calculations based on the semiclassical approach to PCI. Good agreement was found between the calculated and experimental PCI shifts. The result opens possibilities for further studies of the multielectron dynamics between Auger electrons mediated through the photoelectron in these and similar systems.
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9.
  • Kukk, E., et al. (författare)
  • Energy Transfer into Molecular Vibrations and Rotations by Recoil in Inner-Shell Photoemission
  • 2018
  • Ingår i: Physical Review Letters. - : AMER PHYSICAL SOC. - 0031-9007 .- 1079-7114. ; 121:7
  • Tidskriftsartikel (refereegranskat)abstract
    • A mixture of CF4 and CO gases is used to study photoelectron recoil effects extending into the tender xray region. In CF4, the vibrational envelope of the C 1s photoelectron spectrum becomes fully dominated by the recoil-induced excitations, revealing vibrational modes hidden from Franck-Condon excitations. In CO, using CF4 as an accurate energy calibrant, we determine the partitioning of the recoil-induced internal excitation energy between rotational and vibrational excitation. The observed rotational recoil energy is 2.88(28) times larger than the observed vibrational recoil energy, well in excess of the ratio of 2 predicted by the basic recoil model. The experiment is, however, in good agreement with the value of 2.68 if energy transfer via Coriolis coupling is included.
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10.
  • Mailhiot, M., et al. (författare)
  • Multielectron coincidence spectroscopy of the Ar2+(2p-2) double-core-hole decay
  • 2023
  • Ingår i: Physical Review A. - 2469-9926. ; 107:6
  • Tidskriftsartikel (refereegranskat)abstract
    • The dominant decay pathways of argon 2p-2 double-core-hole states have been investigated using synchrotron radiation and a magnetic-bottle-type spectrometer coupled with an ion time-of-flight spectrometer. This experiment allows for efficient multi-electron-ion coincidence measurements, and thus for following the Auger cascade step by step in detail. Dominant decay pathways leading to Ar4+ final states via Ar3+ intermediate states have been assigned with the help of theoretical ab initio calculations. The weak correlated decay of the two core holes by emission of a single Auger electron, leading to Ar3+ final states, has been observed at 458.5-eV kinetic energy. Compared to the total decay of the 2p-2 double core vacancies, this two-electron-one-electron process was measured to have a branching ratio of 1.9 x 10-3 & PLUSMN; 1.0 x 10-3. Furthermore, the remaining decay paths of the Ar1+ (1s-1) core hole to higher charge states and their respective contributions to the total yield have been analyzed and show very good agreement with theoretical results.
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11.
  • Puettner, R., et al. (författare)
  • Double core-hole states in SiX4 (X = F, Cl, Br, and CH3) molecules derived by photoelectron and KLL Auger spectroscopy
  • 2015
  • Ingår i: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 635
  • Tidskriftsartikel (refereegranskat)abstract
    • In recent years double core-hole states are intensively studied since their chemical shifts provide detailed information about initial-state and relaxation effects in a molecule. We derived the Si 1 s(-1), 2s(-1) and 2p(-1) binding energies as well as the Si 2s(-2), 2(p-1)2p(-1), and 2p(-2) double-core hole binding energies of different SiX4 systems in order to derive the chemical shifts. Based on these results we created Wagner plots, which give insight in the initial state and the relaxation effects in the different molecules.
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12.
  • Püttner, R., et al. (författare)
  • Nonstatistical behavior of the photoionization of spin-orbit doublets
  • 2021
  • Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 54:8
  • Tidskriftsartikel (refereegranskat)abstract
    • The photoionization branching ratios of spin-orbit doublets are studied both experimentally and theoretically at energies several keV above threshold. The results show significant relativistic effects for Ar 2p in the autoionizing region below the 1s threshold, and large many-body effects for Xe 3d and 4d in the vicinity of the L-shell thresholds. The branching ratios in Xe are also found to vary significantly over very broad multi-keV energy regions both above and below the inner-shell thresholds. In addition, the Ar 2p study confirms experimentally the decades-old theoretical prediction that the nonresonant branching ratio does not approach the statistical (nonrelativistic) value, and, in fact, progressively diverges from statistical with increasing photon energy. © 2021 The Author(s). Published by IOP Publishing Ltd.
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13.
  • Travnikova, O., et al. (författare)
  • Energy dependent relative cross sections in carbon 1s photoionization
  • 2020
  • Ingår i: 31ST INTERNATIONAL CONFERENCE ON PHOTONIC, ELECTRONIC AND ATOMIC COLLISIONS (ICPEAC XXXI). - : IOP PUBLISHING LTD.
  • Konferensbidrag (refereegranskat)abstract
    • We demonstrate that the possibility of monitoring relative photoionization cross sections over a large photon energy range extending to hard x-rays allows studying and disentangling shake processes and intramolecular inelastic scattering effects. An "EXAFS"-type of oscillatory behaviour of the relative C is cross sections is observed in a wide photon energy range up to 1 keV due to multiple intramolecular elastic scattering of the photoelectron. These effects are also present in solids and constitute a significant part of all elastic and inelastic scattering effects occurring in solids.
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14.
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15.
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16.
  • Boudjemia, N., et al. (författare)
  • Electron spectroscopy and dynamics of HBr around the Br 1s(-1) threshold
  • 2020
  • Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 22:46, s. 26806-26818
  • Tidskriftsartikel (refereegranskat)abstract
    • A comprehensive electron spectroscopic study combined with partial electron yield measurements around the Br 1s ionization threshold of HBr at approximately equal to 13.482 keV is reported. In detail, the Br 1s(-1) X-ray absorption spectrum, the 1s(-1) photoelectron spectrum as well as the normal and resonant KLL Auger spectra are presented. Moreover, the L-shell Auger spectra measured with photon energies below and above the Br 1s(-1) ionization energy as well as on top of the Br 1s(-1)sigma* resonance are shown. The latter two Auger spectra represent the second step of the decay cascade subsequent to producing a Br 1s(-1) core hole. The measurements provide information on the electron and nuclear dynamics of deep core-excited states of HBr on the femtosecond timescale. From the different spectra the lifetime broadening of the Br 1s(-1) single core-hole state as well as of the Br(2s(-2),2s(-1)2p(-1),2p(-2)) double core-hole states are extracted and discussed. The slope of the strongly dissociative HBr 2p(-2)sigma* potential energy curve is found to be about -13.60 eV angstrom(-1). The interpretation of the experimental data, and in particular the assignment of the spectral features in the KLL and L-shell Auger spectra, is supported by relativistic calculations for HBr molecule and atomic Br.
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17.
  • Carniato, S., et al. (författare)
  • Photon-energy dependence of single-photon simultaneous core ionization and core excitation in CO2
  • 2016
  • Ingår i: PHYSICAL REVIEW A. - 2469-9926. ; 94:1
  • Tidskriftsartikel (refereegranskat)abstract
    • We have studied the K-2V process corresponding to simultaneous K-shell ionization and K-shell excitation in the CO2 molecule. We define these K-2V states as super shake-up, at variance with the "conventional" K(-1)v(-1)V shake-up states. While the nature and evolution with photon energy of the conventional shake-up satellites has been the object of many studies, no such data on a large photon-energy range were previously reported on super shake-up. The CO2 molecule is a textbook example because it exhibits two well-isolated K-2V resonances (with V being 2 pi(u)* and 5 delta g*) with different symmetries resulting from shake-up processes of different origin populated in comparable proportions. The variation of the excitation cross section of these two resonances with photon energy is reported, using two different experimental approaches, which sheds light on the excitation mechanisms. Furthermore, double-core-hole spectroscopy is shown to be able to integrate and even expand information provided by conventional single-core-hole X-ray Photoelectron Spectroscopy (XPS) and Near-Edge X-ray Absorption Fine Structure (NEXAFS) techniques, revealing, for instance, g-g dipole forbidden transitions which are only excited in NEXAFS spectra through vibronic coupling.
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18.
  • Ceolin, D., et al. (författare)
  • Auger resonant-Raman study at the Ar K edge as probe of electronic-state-lifetime interferences
  • 2015
  • Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 91:2
  • Tidskriftsartikel (refereegranskat)abstract
    • The resonant-Auger decay in argon following Ar 1s - np excitations was studied under resonant-Raman conditions, i.e., with a total instrumental bandwidth much narrower than the natural linewidth of the absorption features. These state-of-the-art experiments are combined with a radiationless resonant-Raman scattering theory. The main results include identification of the energy position of some high-lying Rydberg states previously masked by insufficient resolution and clear evidence of electronic-state-lifetime interference phenomena.
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19.
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20.
  • Céolin, D., et al. (författare)
  • Far-Zone Resonant Energy Transfer in X-ray Photoemission as a Structure Determination Tool
  • 2017
  • Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 8:12, s. 2730-2734
  • Tidskriftsartikel (refereegranskat)abstract
    • Near-zone Förster resonant energy transfer is the main effect responsible for excitation energy flow in the optical region and is frequently used to obtain structural information. In the hard X-ray region, the Förster law is inadequate because the wavelength is generally shorter than the distance between donors and acceptors; hence, far-zone resonant energy transfer (FZRET) becomes dominant. We demonstrate the characteristics of X-ray FZRET and its fundamental differences with the ordinary near-zone resonant energy-transfer process in the optical region by recording and analyzing two qualitatively different systems: high-density CuO polycrystalline powder and SF6 diluted gas. We suggest a method to estimate geometrical structure using X-ray FZRET employing as a ruler the distance-dependent shift of the acceptor core ionization potential induced by the Coulomb field of the core-ionized donor.
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21.
  • Ceolin, Denis, et al. (författare)
  • Fragmentation of methyl chloride studied by partial positive and negative ion-yield spectroscopy
  • 2007
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 126:8, s. 084309-
  • Tidskriftsartikel (refereegranskat)abstract
    • The authors present partial-ion-yield experiments on the methyl chloride molecule excited in the vicinity of the C12p and C1s inner shells. A large number of fragments, cations produced by dissociation or recombination processes, as well as anionic species, have been detected. Although the spectra exhibit different intensity distributions depending on the core-excited atom, general observations include strong site-selective fragmentation along the C-Cl bond axis and a strong intensity dependence of transitions involving Rydberg series on fragment size.
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22.
  • Céolin, D., et al. (författare)
  • Ultrafast Charge Transfer Processes Accompanying KLL Auger Decay in Aqueous KCl Solution
  • 2017
  • Ingår i: Physical Review Letters. - 0031-9007. ; 119:26
  • Tidskriftsartikel (refereegranskat)abstract
    • X-ray photoelectron and KLL Auger spectra were measured for the K+ and Cl- ions in aqueous KCl solution. While the XPS spectra of these ions have similar structures, both exhibiting only weak satellites near the main line, the Auger spectra differ dramatically. Contrary to the chloride case, a very strong extra peak was found in the Auger spectrum of K+ at the low kinetic energy side of the D1 state. Using the equivalent core model and ab initio calculations this spectral feature was assigned to electron transfer processes from solvent water molecules to the solvated cation. The observed charge transfer processes are suggested to play an important role in charge redistribution following single and multiple core-hole creation in atoms and molecules placed into environment.
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23.
  • Goldsztejn, G., et al. (författare)
  • Double-Core-Hole States in Neon: Lifetime, Post-Collision Interaction, and Spectral Assignment
  • 2016
  • Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 117:13
  • Tidskriftsartikel (refereegranskat)abstract
    • Using synchrotron radiation and high-resolution electron spectroscopy, we have directly observed and identified specific photoelectrons from K-2V states in neon corresponding to simultaneous 1s ionization and 1s -> valence excitation. The natural lifetime broadening of the K-2V states and the relative intensities of different types of shakeup channels have been determined experimentally and compared to ab initio calculations. Moreover, the high-energy Auger spectrum resulting from the decay of Ne2+K-2 and Ne+K-2V states as well as from participator Auger decay from Ne+K-1L-1V states, has been measured and assigned in detail utilizing the characteristic differences in lifetime broadenings of these core hole states. Furthermore, post collision interaction broadening of Auger peaks is clearly observed only in the hypersatellite spectrum from K-2 states, due to the energy sharing between the two 1s photoelectrons which favors the emission of one slow and one fast electron.
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24.
  • Goldsztejn, G., et al. (författare)
  • Electronic-state-lifetime interference in the hard-x-ray regime : Argon as a showcase
  • 2017
  • Ingår i: PHYSICAL REVIEW A. - : AMER PHYSICAL SOC. - 2469-9926. ; 95:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Electronic-state-lifetime interference is a phenomenon specific for ionization of atoms and molecules in the hard-x-ray regime. Using resonant KL2,3L2,3 Auger decay in argon as a showcase, we present a model that allows extracting the interference terms directly from the cross sections of the final electronic states. The analysis provides fundamental information on the excitation and decay processes such as probabilities of various decay paths and the values of the dipole matrix elements for transitions to the excited states. Our results shed light on the interplay between spectator, shake-down, and shake-up processes in the relaxation of deep core-hole states.
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25.
  • Goldsztejn, G., 2017, et al. (författare)
  • Experimental and theoretical study of the double-core-hole hypersatellite Auger spectrum of Ne
  • 2017
  • Ingår i: Physical Review A. - : AMER PHYSICAL SOC. - 2469-9926 .- 2469-9934. ; 96
  • Tidskriftsartikel (refereegranskat)abstract
    • We present the hypersatellite Auger spectrum of neon which contains the decay transitions of the K−2, K−2V, K−2L−1, K−2L−1V, and K−1L−1V states. The Auger decays of these types of core-hole states show different line shapes and linewidths which can be distinguished due to the high experimental resolution available for the present experiments. The individual Auger transitions are assigned based on various approaches. Complementary calculations are performed to assign the K−2L−1 → K−1L−3 and the K−2L−1V → K−1L−3V Auger transitions. Based on the obtained results we were able to derive the ratio for the double to single ionization yield.
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26.
  • Goldsztejn, G., et al. (författare)
  • Simulation of Auger decay dynamics in the hard X-ray regime : HCl as a showcase
  • 2022
  • Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 24:11, s. 6590-6604
  • Tidskriftsartikel (refereegranskat)abstract
    • Auger decay after photoexcitation or photoemission of an electron from a deep inner shell in the hard X-ray regime can be rather complex, implying a multitude of phenomena such as multiple-step cascades, post-collision interaction (PCI), and electronic state-lifetime interference. Furthermore, in a molecule nuclear motion can also be triggered. Here we discuss a comprehensive theoretical method which allows us to analyze in great detail Auger spectra measured around an inner-shell ionization threshold. HCl photoexcited or photoionized around the deep Cl 1s threshold is chosen as a showcase. Our method allows calculating Auger cross sections considering the nature of the ground, intermediate and final states (bound or dissociative), and the evolution of the relaxation process, including both electron and nuclear dynamics. In particular, we show that we can understand and reproduce a so-called experimental 2D-map, consisting of a series of resonant Auger spectra measured at different photon energies, therefore obtaining a detailed picture of all above-mentioned dynamical phenomena at once.
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27.
  • Goldsztejn, G., et al. (författare)
  • Ultrafast Dynamics And Electronic State - Lifetime Interferences In Chlorine-Containing Molecules
  • 2015
  • Ingår i: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 635
  • Tidskriftsartikel (refereegranskat)abstract
    • In order to have access to fine phenomena such as ultrafast nuclear dynamics and electronic state - lifetime interferences (ELI) at high energies (few keV), one has to rely on great experimental resolution. The new experimental HAXPES endstation at the GALAXIES beamline of the French synchrotron SOLEIL provides photons in the 2-12 keV energy range along with a total instrumental resolution below 500 meV. In this work we show experimental evidences of ultrafast nuclear dynamics and ELI on HCl and CH3Cl excited around the Cl 1s resonance. We show also simulations that allow to disentangle the contribution of nuclear dynamics and ELI in our experimental spectra.
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28.
  • Gopakumar, Geethanjali, 1992-, et al. (författare)
  • Non-local decay of highly charged aqueous inorganic ions produced by Auger decay
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • High-Z atoms are more important for biological radiation damage by photons than their low abundance due to their higher photoionization cross-section. Using the inorganic Mg 2+ and Al3+ ions in water as model systems, we have studied decay processes following deep core-level ionization. Local Auger decay rapidly produces highly charged Mg 4+and Al5+ ions, the decay of which must involve non-local processes involving the surrounding water, such as electron transfer mediated decay (ETMD). Using electron spectroscopy we observe two distinct ETMD decay steps for Al, corresponding to decay from Al5+ to Al4+, and then from Al4+ to Al3+. The ETMD energetics is discussed using both a simple model and calculations. Contrary to expectations, we do not observe any ETMD for Mg, and possible reasons for this are discussed.
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29.
  • Gopakumar, Geethanjali, 1992-, et al. (författare)
  • Probing Aqueous Ions with Non-local Auger Relaxation
  • 2022
  • Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 24:15, s. 8661-8671
  • Tidskriftsartikel (refereegranskat)abstract
    • The decay of core holes is often regarded as a local process, but in some systems, it involves the autoionization of neighbouring atoms or molecules. Here, we explore such non-local autoionization (Intermolecular Coulombic Decay, ICD) of surrounding molecules upon 1s ionization of aqueous-phase Na+, Mg2+ and Al3+ ions. The three ions are isoelectronic but differ in the strength of the ion-water interactions which is manifested in experimental Auger electron spectra by varying intensities. While for strongly interacting Mg2+ and Al3+ the non-local decay is observed, for weakly bound Na+ no signal was measured. Combined with theoretical simulations we provide a microscopic understanding of the non-local decay processes. We assigned the ICD to decay processes ending with two-hole states delocalized between the central ion and neighbouring water. The ICD process is also shown to be highly selective with respect to water molecular orbitals. The ICD lifetime was estimated to be around 40 fs for Mg and 20 fs for Al. Auger spectroscopy thus represents a novel tool for exploring molecules in the liquid phase, providing simultaneously structural and electronic information.   
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30.
  • Gopakumar, G., et al. (författare)
  • Radiation damage by extensive local water ionization from two-step electron-transfer-mediated decay of solvated ions
  • 2023
  • Ingår i: Nature Chemistry. - : Nature Publishing Group. - 1755-4330 .- 1755-4349. ; 15:10, s. 1408-1414
  • Tidskriftsartikel (refereegranskat)abstract
    • Biomolecular radiation damage is largely mediated by radicals and low-energy electrons formed by water ionization rather than by direct ionization of biomolecules. It was speculated that such an extensive, localized water ionization can be caused by ultrafast processes following excitation by core-level ionization of hydrated metal ions. In this model, ions relax via a cascade of local Auger–Meitner and, importantly, non-local charge- and energy-transfer processes involving the water environment. Here, we experimentally and theoretically show that, for solvated paradigmatic intermediate-mass Al3+ ions, electronic relaxation involves two sequential solute–solvent electron transfer-mediated decay processes. The electron transfer-mediated decay steps correspond to sequential relaxation from Al5+ to Al3+ accompanied by formation of four ionized water molecules and two low-energy electrons. Such charge multiplication and the generated highly reactive species are expected to initiate cascades of radical reactions. [Figure not available: see fulltext.]
  •  
31.
  • Gopakumar, Geethanjali, et al. (författare)
  • X-ray-induced attosecond ion-water electron dynamics of aqueous ions
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • The foundation of many physical and chemical processes is the transfer of charge from one entity to another. In many cases, the charge transfer is mediated by electron transfer and due to the comparatively low mass of electrons, these processes tend to take place within a few femtoseconds or several attoseconds. We investigate the charge transfer from Na+, Mg2+ and Al3+ in an aqueous environment to neighbouring water molecules. In order to achieve this, we use the core-hole clock method and Auger spectroscopy upon 1s ionization of the respective ions. The charge transfer times range from several 100 as below the 1s ionization threshold to only 20 as far above the 1s ionization. The decrease in charge transfer times as a function of the photon energy seems to be continuous. Despite the ions being isoelectronic in our study, we nd differences in their charge transfer behaviour.
  •  
32.
  • Guillemin, R., et al. (författare)
  • Interplay of complex decay processes after argon 1s ionization
  • 2018
  • Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : AMER PHYSICAL SOC. - 2469-9926 .- 2469-9934. ; 97:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Complex decay pathways involving radiative and nonradiative relaxation after deep core-level ionization in argon are disentangled by a unique combination of several synchrotron radiation-based spectroscopic techniques. In particular, by comparing the results obtained from electron-ion coincidence, photon-ion coincidence, and x-ray emission measurements, we are able to distinguish the final ionic states produced in the cascade decay involving K alpha and K beta radiative decay and final ionic states produced by nonradiative cascade decay. High-resolution Auger electron spectroscopy is then used as a complementary tool to identify the LMM transitions contributing to the cascade decay. Ab initio calculations are performed to identify the electronic states involved in the LMM decay.
  •  
33.
  • Guillemin, R., et al. (författare)
  • Postcollision interaction effects in KLL Auger spectra following argon 1s photoionization
  • 2015
  • Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 92:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Postcollision interaction effects on the Auger decay of a deep core hole are studied both experimentally and theoretically. KL2,L-3(2),(3) decay spectra of the Ar 1s vacancy are measured with high-energy resolution with excess photon energies ranging from 0 to 200 eV above the ionization threshold. Interaction of the Auger electron with the photoelectron and the ion field manifests itself in the Auger spectra as a distortion of the energy distribution of the Auger electron close to threshold. Moreover, recapture of the photoelectron due to energy exchange is dominating in the low-photon-energy range above threshold. The experimental results are compared with calculations based on the semiclassical approach to the postcollision interaction. The energies of the discrete levels and individual recapture cross sections are computed in the Hartree-Fock approximation. Good agreement is found between the calculated and experimental spectra, validating the model used.
  •  
34.
  • Journel, Loïc, et al. (författare)
  • Resonant double Auger decay in carbon K-shell excitation of CO
  • 2008
  • Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 77:4, s. 14-042710
  • Tidskriftsartikel (refereegranskat)abstract
    • We have studied double Auger decay after C 1s→2 photoexcitation in gas phase carbon monoxide. Two distinct processes, namely direct double Auger decay and cascade double Auger decay, are identified and studied in detail using multiple coincidence techniques. Cascade Auger decay is shown to be the overall dominant process. Decay channels involving the dissociation of the molecule followed by autoionization of the oxygen fragments are observed.
  •  
35.
  • Koulentianos, Dimitris, 1987, et al. (författare)
  • Double-core-hole states in CH3CN: Pre-edge structures and chemical-shift contributions
  • 2018
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 149
  • Tidskriftsartikel (refereegranskat)abstract
    • Spectra reflecting the formation of single-site double-core-hole pre-edge states involving the N 1s and C 1s core levels of acetonitrile have been recorded by means of high-resolution single-channel photoelectron spectroscopy using hard X-ray excitation. The data are interpreted with the aid of ab initio quantum chemical calculations, which take into account the direct or conjugate nature of this type of electronic states. Furthermore, the photoelectron spectra of N 1s and C 1s singly core-ionized states have been measured. From these spectra, the chemical shift between the two C 1s(-1) states is estimated. Finally, by utilizing C 1s single and double core-ionization potentials, initial and final state effects for the two inequivalent carbon atoms have been investigated. Published by AIP Publishing.
  •  
36.
  • Koulentianos, Dimitris, 1987, et al. (författare)
  • KL double core hole pre-edge states of HCl
  • 2018
  • Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 20:4
  • Tidskriftsartikel (refereegranskat)abstract
    • The formation of double core hole pre-edge states of the form $1s^{-1}2p^{-1}(^{1,3}\text{P})\sigmaup^*,n\ell$ for HCl, located on the binding energy scale as deep as 3 keV, has been investigated by means of a high resolution single channel electron spectroscopy technique recently developed for the hard x-ray region. A detailed spectroscopic assignment is performed based on \textit{ab initio} quantum chemical calculations and by using a sophisticated fit model comprising regular Rydberg series. Quantum defects for the different Rydberg series are extracted and the energies for the associated double core hole ionization continua are extrapolated. Dynamical information such as the lifetime width of these double-core-hole pre-edge states and the slope of the related dissociative potential energy curves are also obtained. In addition, $1s^{-1}2p^{-1}V^{-1}n\ell\lambdaup n^{\prime}\ell^{\prime}\lambdaup^{\prime}$ double shake-up transitions and double core hole states of the form $1s^{-1}2s^{-1}(^{1,3}\text{S})\sigmaup^*,4s$ are observed.
  •  
37.
  • Koulentianos, Dimitris, 1987, et al. (författare)
  • The O K-2V spectrum of CO: the influence of the second core-hole
  • 2021
  • Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 18, s. 10780-90
  • Tidskriftsartikel (refereegranskat)abstract
    • Using synchrotron radiation in the tender X-ray regime, a photoelectron spectrum showing the formation of single site double-core-hole pre-edge states, involving the K shell of the O atom in CO, has been recorded by means of high-resolution electron spectroscopy. The experimentally observed structures have been simulated, interpreted and assigned, employing state-of-the-art ab initio quantum chemical calculations, on the basis of a theoretical model, accounting for their so-called direct or conjugate character. Features appearing above the double ionization threshold have been reproduced by taking into account the strong mixing between multi-excited and continuum states. The shift of the sigma* resonance below the double ionization threshold, in combination with the non-negligible contributions of multi-excited configurations in the final states reached, gives rise to a series of avoided crossings between the different potential energy curves.
  •  
38.
  • Kukk, E., et al. (författare)
  • Unified treatment of recoil and Doppler broadening in molecular high-energy photoemission
  • 2021
  • Ingår i: New Journal of Physics. - : Institute of Physics Publishing (IOPP). - 1367-2630. ; 23:6
  • Tidskriftsartikel (refereegranskat)abstract
    • Doppler and recoil effects are an integral part of the photoemission process at the high kinetic energies reached in hard x-ray photo-electron spectroscopy (HAXPES) and have a major effect on the observed lineshape, resulting in broadening, energy losses and discrete excitations. These effects can be modeled with a high degree of detail for small systems like diatomic molecules, for larger systems such treatment is often superfluous as the fine spectral features are not observable. We present a united description of the Doppler and recoil effects for arbitrary polyatomic systems and offer an approximate description of the recoil- and Doppler-modified photoemission spectral lineshape as a practical tool in the analysis of HAXPES spectra of core-level photoemission. The approach is tested on the examples of carbon dioxide and pentane molecules. The C and O 1s photoelectron spectra of CO2 in gas phase were also measured at 2.3 and 7.0 keV photon energy at Synchrotron SOLEIL and the spectra were analyzed using the model description. The limitations and applicability of the approach to adsorbates, interfaces and solids is briefly discussed.
  •  
39.
  • Kushawaha, R. K., et al. (författare)
  • Auger resonant-Raman decay after Xe L-edge photoexcitation
  • 2015
  • Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 92:1
  • Tidskriftsartikel (refereegranskat)abstract
    • We have investigated resonant Auger decay of xenon following photoexcitation of each of the three L edges under resonant-Raman conditions, which allowed us to characterize several higher Rydberg transitions. Relative intensities for spectator final states reached after L-1-, L-2-, and L-3-edge excitations are studied in detail. Thanks to state-of-the-art experimental arrangements, our results not only reproduce the previously calculated 3d(-2)5d and nd (n > 5) state cross sections after L-3 excitation, but also allow extracting the 3d(-2)6d spectator state energy position and revealing its resonant behavior, blurred by the insufficient experimental resolution in previous data sets. The 3d(-2)6p and 3d(-2)7p states reached after L-1 excitation as well as the 3d(-2)5d and 3d(-2)6d states reached after L-2 excitation are also investigated and their relative intensities are reported and compared to ab initio Dirac-Hartree-Fock configuration-interaction calculations. We found the signature of electronic-state-lifetime interference effects between several coherently excited intermediate states, due to large lifetime broadening. Electron recapture processes are also identified above all three photoionization thresholds.
  •  
40.
  • Laksman, Joakim, et al. (författare)
  • Role of the Renner-Teller effect after core hole excitation in the dissociation dynamics of carbon dioxide dication.
  • 2012
  • Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 136:10
  • Tidskriftsartikel (refereegranskat)abstract
    • The fragmentation of the doubly-charged carbon dioxide molecule is studied after photoexcitation to the C 1s(1)2π(u) and O 1s(1)2π(u) states using a multicoincidence ion-imaging technique. The bent component of the Renner-Teller split states populated in the 1s→ π∗ resonant excitation at both the carbon and oxygen 1s ionization edges opens pathways to potential surfaces in highly bent geometries in the dication. Evidence for a complete deformation of the molecule is found in the coincident detection of C(+) and O(2) (+) ions. The distinct alignment of this fragmentation channel indicates rapid deformation and subsequent fragmentation. Investigation of the complete atomization dynamics in the dication leading to asymmetric charge separation shows that the primary dissociation mechanisms, sequential, concerted, and asynchronous concerted, are correlated to specific fragment kinetic energies. The study shows that the bond angle in fragmentation can extend below 20°.
  •  
41.
  • Marchenko, T., et al. (författare)
  • Potential Energy Surface Reconstruction and Lifetime Determination of Molecular Double-Core-Hole States in the Hard X-Ray Regime
  • 2017
  • Ingår i: Physical Review Letters. - : AMER PHYSICAL SOC. - 0031-9007 .- 1079-7114. ; 119:13
  • Tidskriftsartikel (refereegranskat)abstract
    • A combination of resonant inelastic x-ray scattering and resonant Auger spectroscopy provides complementary information on the dynamic response of resonantly excited molecules. This is exemplified for CH3I, for which we reconstruct the potential energy surface of the dissociative I 3d(-2) double-core-hole state and determine its lifetime. The proposed method holds a strong potential for monitoring the hard x-ray induced electron and nuclear dynamic response of core-excited molecules containing heavy elements, where ab initio calculations of potential energy surfaces and lifetimes remain challenging.
  •  
42.
  • Marchenko, T., et al. (författare)
  • Single and multiple excitations in double-core-hole states of free water molecules
  • 2020
  • Ingår i: Journal of Physics B-Atomic Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 53:22
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a combined experimental and theoretical study of the double-core-hole photoelectron spectrum obtained in isolated water molecules irradiated with hard x-rays above the oxygen K -2 threshold. States of the type O K -2V and multiply excited states are created by single-photon absorption and subsequent one-electron emission. A detailed analysis enabled by high experimental resolution reveals dissociative nuclear dynamics in the K-2V pre-edge states. At the binding energies above the K- 2 double-ionization potential, a complex spectral pattern is observed and attributed to highly excited states involving multiple shake-up excitation processes with the aid of state- of-the-art theoretical calculations. A strong broadening due to the nuclear motion indicates a highly dissociative nature of these multiply excited states, in agreement with the theoretical analysis.
  •  
43.
  • Marchenko, T., et al. (författare)
  • Ultrafast nuclear dynamics in the doubly-core-ionized water molecule observed via Auger spectroscopy
  • 2018
  • Ingår i: Physical Review A. - : AMER PHYSICAL SOC. - 2469-9926 .- 2469-9934. ; 98:6
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a combined experimental and theoretical study of the Auger-emission spectrum following double core ionization and excitation of gas-phase water molecules with hard-x-ray synchrotron radiation above the O K-2 threshold. We observe an indication of ultrafast proton motion occurring within the 1.5 fs lifetime of the double-core-hole (DCH) states in water. Furthermore, we have identified symmetric and antisymmetric dissociation modes characteristic for particular DCH states. Our results serve as a fundamental reference for state-of-the-art studies of DCH dynamic processes in liquid water both at synchrotron and free-electron-laser facilities.
  •  
44.
  • Martins, J. B., et al. (författare)
  • Electron delocalisation in conjugated sulfur heterocycles probed by resonant Auger spectroscopy
  • 2022
  • Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 24:14, s. 8477-8487
  • Tidskriftsartikel (refereegranskat)abstract
    • We propose a novel approach for an indirect probing of conjugation and hyperconjugation in core-excited molecules using resonant Auger spectroscopy. Our work demonstrates that the changes in the electronic structure of thiophene (C4H4S) and thiazole (C3H3NS), occurring in the process of resonant sulfur K-shell excitation and Auger decay, affect the stabilisation energy resulting from pi-conjugation and hyperconjugation. The variations in the stabilisation energy manifest themselves in the resonant S KL2,3L2,3 Auger spectra of thiophene and thiazole. The comparison of the results obtained for the conjugated molecules and for thiolane (C4H8S), the saturated analogue of thiophene, has been performed. The experimental observations are interpreted using high-level quantum-mechanical calculations and the natural bond orbital analysis.
  •  
45.
  •  
46.
  • Piancastelli, Maria Novella, et al. (författare)
  • Partial cation and anion-yield experiments in ammonia around the N 1s ionization threshold
  • 2007
  • Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 155:1-3, s. 86-90
  • Tidskriftsartikel (refereegranskat)abstract
    • We report partial cation and anion-yield measurements around the N K edge in isolated ammonia molecules. Due to the dominance of spectator electronic decay following Rydberg excitations, fragmentation was found to be more extensive following excitation to intermediate states of Rydberg character compared to excitation of states with molecular-orbital character. Unusual stability of the NH32+ fragment produced directly above threshold by normal-Auger decay is attributed to a stable planar geometry induced by a specific electronic configuration. Hydrogen anions are not detected above threshold except following the decay of resonant doubly excited neutral states embedded in the K-shell ionization continuum.
  •  
47.
  • Puettner, R., et al. (författare)
  • Detailed assignment of normal and resonant Auger spectra of Xe near the L edges
  • 2017
  • Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - 2469-9926 .- 2469-9934. ; 96:2
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a comprehensive experimental and theoretical investigation on the LMM, LMN, and LNN normal Auger spectra of xenon, which reveal excellent agreement with theory when core-hole lifetimes of the two-hole final states are taken into account. Generally, the spectra turned out to be highly complex due to a strong overlap of the Auger transitions subsequent to 2s(1/2)(-1), 2p(1/2)(-1), and 2p(3/2)(-1) ionization. This overlap is due to the splitting of the three initial L core holes and the different final M and N core holes being on the same order of magnitude of several hundred eV. The Auger transitions are assigned in detail based on the theoretical results. Most of the MM, MN, and NN final states are described well based on jj coupling. In addition, we present a detailed assignment of the resonant LM45M45 Auger transition subsequent to the 2s -> 6p, 7p and 2p -> 5d, 6d excitations.
  •  
48.
  • Puettner, R., et al. (författare)
  • Hidden double excitations in the oxygen inner-shell ionization continuum of CO
  • 2013
  • Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 15, s. 033003-
  • Tidskriftsartikel (refereegranskat)abstract
    • Auger decay spectra of CO subsequent to O 1s ionization with 549.85 eV photons, i.e. close to the top of the shape resonance, are presented. Their comparison with the normal Auger spectrum recorded at a photon energy well above the shape resonance reveals distinct features. In particular, in the energy region of the O 1s(-1) -> b(1)Pi and O 1s(-1) -> a(1)Sigma(+) Auger transitions which are well known to consist of vibrational progressions, additional narrow lines are revealed by the spectra recorded at 549.85 eV. In a detailed fit analysis of these Auger spectra it was possible to show that the newly found lines do not exhibit the expected distortions caused by post-collision interaction. This observation identifies these lines as caused by a different mechanism, such as resonant Auger decay processes of doubly excited states. The transitions are assigned using energy and intensity arguments in combination with complementary angular distribution measurements for the Auger electrons.
  •  
49.
  • Puttner, R., et al. (författare)
  • Argon 1s(-2) Auger hypersatellites
  • 2020
  • Ingår i: Journal of Physics B-Atomic Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 54:2
  • Tidskriftsartikel (refereegranskat)abstract
    • The 1s(-2) Auger hypersatellite spectrum of argon is studied experimentally and theoretically. In total, three transitions to the final states 1s(-1)2p(-2)(S-2(e),D-2(e)) and 1s(-1)2s(-1)(S-1)2p(-1)(P-2(o)) are experimentally observed. The lifetime broadening of the 1s(-2) -> 1s(-1)2p(-2)(S-2(e),D-2(e)) states is determined to be 2.1(4) eV. For the used photon energy of h nu = 7500 eV a KK/K ionisation ratio of 2.5(3) x 10(-4) is derived. Generally, a good agreement between the experimental and present theoretical energy positions, linewidths, and intensities is obtained.
  •  
50.
  • Püttner, R., et al. (författare)
  • Argon KLL Auger spectrum: Initial states, core-hole lifetimes, shake, and knock-down processes
  • 2020
  • Ingår i: Physical Review A. - : AMER PHYSICAL SOC. - 2469-9926 .- 2469-9934. ; 102:5
  • Tidskriftsartikel (refereegranskat)abstract
    • State-of-the-art argon KLL Auger spectra measured using photon energies of hν=3216 and 3400 eV are presented along with an Ar [1s] photoelectron spectrum (square brackets indicate holes in the respective orbital). The two different photon energies used for measuring the Auger spectra allow distinguishing between the shake transitions during the Auger decay and the Auger transitions of the photoelectron satellites. A complete assignment of satellite transitions is provided, partially based on configuration-interaction calculations. In addition, Ar [1s3(s,p)]n′l′→[2p2(1D2)] transitions are observed, which can be explained by knock-down transitions leading to a direct exchange of angular momentum between the excited electron and the Auger electron. The lifetime broadenings of the Ar [2s] single-core-hole state and the [2s2] and [2s2p] double-core-hole states are also determined, confirming previously observed trends for double-core-hole states. © 2020 American Physical Society.
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