| 1. |
- Andersson, Jonas, et al.
(författare)
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Auger decay of 4d inner-shell holes in atomic Hg leading to triple ionization
- 2017
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Ingår i: Physical Review A. - : AMER PHYSICAL SOC. - 2469-9926 .- 2469-9934. ; 96
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Tidskriftsartikel (refereegranskat)abstract
- Formation of triply ionized states upon the creation of 4d inner-shell holes in atomic Hg is investigated by using synchrotron radiation of 730 eV photon energy and a versatile multielectron coincidence detection technique in combination with multiconfiguration Dirac-Fock calculations. By carefully selecting Coster-Kronig electrons detected only in coincidence with a 4d photoelectron, the Coster-Kronig spectrum has been extracted and the corresponding branching ratios of the 4d hole have been determined. The results are found to differ from previously established experimental ratios based on electron impact ionization but to agree now better with theory. We also present an Auger cascade analysis of pathways leading to triply ionized states of atomic Hg upon removal of a 4d inner-shell electron.
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| 2. |
- Andersson, Jonas, et al.
(författare)
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Parametrization of energy sharing distributions in direct double photoionization of He
- 2019
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- We present experimental results on the characteristic sharing of available excess energy, ranging from 11–221eV, between two electrons in single-photon direct double ionization of He. An effective parametrization of the sharing distributions is presented along with an empirical model that describes the complete shape of the distribution based on a single experimentally determinable parameter. The measured total energy sharing distributions are separated into two distributions representing the shake-off and knock-out parts by simulating the sharing distribution curves expected from a pure wave collapse after a sudden removal of the primary electron. In this way, empirical knock-out distributions are extracted and both the shake-off and knock-out distributions are parametrized. These results suggest a simple method that can be applied to other atomic and molecular systems to experimentally study important aspects of the direct double ionization process.
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| 3. |
- Boudjemia, N., et al.
(författare)
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Electron spectroscopy and dynamics of HBr around the Br 1s(-1) threshold
- 2020
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 22:46, s. 26806-26818
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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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| 4. |
- Feifel, Raimund, et al.
(författare)
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Cationic double K-hole pre-edge states of CS2 and SF6
- 2017
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 7
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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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| 5. |
- Hult Roos, Andreas, et al.
(författare)
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Abundance of molecular triple ionization by double Auger decay
- 2018
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Systematic measurements of electron emission following formation of single 1s or 2p core holes in molecules with C, O, F, Si, S and Cl atoms show that overall triple ionization can make up as much as 20% of the decay. The proportion of triple ionization is observed to follow a linear trend correlated to the number of available valence electrons on the atom bearing the initial core hole and on closest neighbouring atoms, where the interatomic distance is assumed to play a large role. The amounts of triple ionization (double Auger decay) after 1s or 2p core hole formation follow the same linear trend, which indicates that the hole identity is not a crucial determining factor in the number of electrons emitted. The observed linear trend for the percentage of double Auger decay follows a predictive line equation of the form DA = 0.415 · Nve + 5.46.
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| 6. |
- Hult Roos, Andreas, et al.
(författare)
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Valence double ionization electron spectra of CH3F, CH3Cl and CH3I
- 2017
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Ingår i: Chemical Physics. - : Elsevier BV. - 0301-0104 .- 1873-4421. ; 491, s. 42-47
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Tidskriftsartikel (refereegranskat)abstract
- Valence double ionization electron spectra of the methyl fluoride, methyl chloride, and methyl iodide molecules have been recorded using a time-of-flight photoelectron-photoelectron coincidence technique. The spectra are interpreted by comparison with existing ionization data, Auger spectra, and theoretical calculations. The lowest double ionization energies have been found to be around 35.0 eV, 30.6 eV, and 26.67 eV for CH3F, CH3Cl and CH3I, respectively. These energies are also compared with the predictions and implications of an empirical rule for the lowest double ionization energy in molecules.
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| 7. |
- Koulentianos, Dimitris, 1987, et al.
(författare)
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Double-core-hole states in CH3CN: Pre-edge structures and chemical-shift contributions
- 2018
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 149
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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.
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| 8. |
- Koulentianos, Dimitris, 1987
(författare)
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Double Inner-Shell Vacancies in Molecules
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Molecular electronic states possessing a double core-vacancy, referred to as double-core-hole (DCH) states, were predicted more than thirty years ago, to have interesting properties, which would allow one to probe matter in a much more detailed way compared to conventional single core-vacancy techniques. Though DCH states are characterized by low cross-sections compared to the dominant single-core-hole (SCH) states, which implies experimental challenges, the development of third generation synchrotron radiation (SR) facilities and X-ray free electron lasers (XFEL), in combination with advanced spectroscopy techniques, resulted recently in a significant number of scientific works reporting on the observation of different types of DCH states. Within the framework of this thesis, experimental work in terms of high resolution single channel electron spectroscopy was carried out, detecting DCH states of the form K-1L-1V, where one core electron has been ionized and the second has been excited to an unoccupied orbital V. One example concerns the case of HCl, where the experimental spectrum has been reproduced by a fit model taking into account Rydberg series within different spin-orbit multiplicities. From this analysis, the thresholds for the double ionization continua and the quantum defects for different Rydberg electrons have been extrapolated. Furthermore, electron spectra reflecting the formation of K-2V DCH states, which involve the K shells of the N and C atoms in CH3CN, have also been recorded and interpreted based on a theoretical model considering the direct (dipolar ionization - monopolar excitation) or the conjugate (dipolar excitation - monopolar ionization) nature of each observed transition. In addition, the initial and final state effects contributing to the chemical shift between the two non-equivalent C atoms have been discussed and visualized by employing a Wagner plot. Related results are reported on the formation of K-2V DCH states in SF6 and CS2. The influence of the slope of the potential energy curve on the broadening of the spectral features is discussed along with the appearance of a pronounced background. Fingerprints of nuclear dynamics upon the decay of several types of DCH states in H2O have been identified by recording the related hyper-satellite Auger spectrum. Complementary, the technique of multi-electron coincidence spectroscopy was used for the study of the formation of K-2V and K-2 DCH states in C4H10, where the latter type of DCHs with both core electrons being ejected to the continuum, has been measured directly and in the same experiment as the K-2V states.
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| 9. |
- Koulentianos, Dimitris, 1987, et al.
(författare)
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Formation and relaxation of K-2 and K-2V double-core-hole states in n-butane
- 2022
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 157:4
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Tidskriftsartikel (refereegranskat)abstract
- Using a magnetic bottle multi-electron time-of-flight spectrometer in combination with synchrotron radiation, double-core-hole pre-edge and continuum states involving the K-shell of the carbon atoms in n-butane ( n-C4H10) have been identified, where the ejected core electron(s) and the emitted Auger electrons from the decay of such states have been detected in coincidence. An assignment of the main observed spectral features is based on the results of multi-configurational self-consistent field (MCSCF) calculations for the excitation energies and static exchange (STEX) calculations for energies and intensities. MCSCF results have been analyzed in terms of static and dynamic electron relaxation as well as electron correlation contributions to double-core-hole state ionization potentials. The analysis of applicability of the STEX method, which implements the one-particle picture toward the complete basis set limit, is motivated by the fact that it scales well toward large species. We find that combining the MCSCF and STEX techniques is a viable approach to analyze double-core-hole spectra.
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| 10. |
- Koulentianos, Dimitris, 1987, et al.
(författare)
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KL double core hole pre-edge states of HCl
- 2018
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 20:4
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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.
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| 11. |
- Koulentianos, Dimitris, 1987, et al.
(författare)
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The O K-2V spectrum of CO: the influence of the second core-hole
- 2021
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 18, s. 10780-90
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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.
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| 12. |
- Marchenko, T., et al.
(författare)
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Single and multiple excitations in double-core-hole states of free water molecules
- 2020
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Ingår i: Journal of Physics B-Atomic Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 53:22
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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.
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| 13. |
- Marchenko, T., et al.
(författare)
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Ultrafast nuclear dynamics in the doubly-core-ionized water molecule observed via Auger spectroscopy
- 2018
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Ingår i: Physical Review A. - : AMER PHYSICAL SOC. - 2469-9926 .- 2469-9934. ; 98:6
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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.
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| 14. |
- Martins, J. B., et al.
(författare)
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Electron delocalisation in conjugated sulfur heterocycles probed by resonant Auger spectroscopy
- 2022
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 24:14, s. 8477-8487
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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.
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| 15. |
- Puttner, R., et al.
(författare)
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Argon 1s(-2) Auger hypersatellites
- 2020
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Ingår i: Journal of Physics B-Atomic Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 54:2
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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.
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| 16. |
- Püttner, R., et al.
(författare)
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Argon KLL Auger spectrum: Initial states, core-hole lifetimes, shake, and knock-down processes
- 2020
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Ingår i: Physical Review A. - : AMER PHYSICAL SOC. - 2469-9926 .- 2469-9934. ; 102:5
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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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| 17. |
- Püttner, R., et al.
(författare)
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Nonstatistical behavior of the photoionization of spin-orbit doublets
- 2021
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 54:8
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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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| 18. |
- Santos, A. C. F., et al.
(författare)
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Resonant Auger decay induced by the symmetry-forbidden 1a(1g)? 6a(1g) transition of the SF6 molecule
- 2022
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Ingår i: Journal of Vacuum Science & Technology A. - : American Vacuum Society. - 0734-2101 .- 1520-8559. ; 40:4
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Tidskriftsartikel (refereegranskat)abstract
- Resonant Auger electron spectroscopic study at the symmetry-forbidden 1 a 1 g -> 6 a 1 g excitation below the S K-shell threshold of SF 6 is reported. Partial electron yield and resonant K L L Auger spectra have been measured by using monochromatized undulator synchrotron radiation. By changing the photon energy in small steps, a so-called 2D map is produced. In this map, the dipole-forbidden transition exhibits spectral features (e.g., an S-shaped dispersion relation), which are well known and understood for dipole-allowed transitions. We validate by a theory that for the case of dipole-forbidden transitions, these spectral features can be analyzed in the same way as previously established for the dipole-allowed ones. This approach grants information on the nuclear dynamics in the K-shell core-excited states of SF 6 on the femtosecond (fs) timescale. In particular, for the potential-energy curves of the states S 1 s(-1) 6(a1g) and S 2p(-2)6a(1g), the slopes at the equilibrium distance of the ground state are derived. Symmetry breaking as a result of ultrafast vibronic coupling is revealed by the population of the electronically forbidden excited state. Published under an exclusive license by the AVS.
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| 19. |
- Velasquez, Nicolas, et al.
(författare)
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X-ray induced ultrafast charge transfer in thiophene-based conjugated polymers controlled by core-hole clock spectroscopy
- 2024
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Ingår i: Physical Chemistry Chemical Physics. - 1463-9076 .- 1463-9084. ; 26:2, s. 1234-1244
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Tidskriftsartikel (refereegranskat)abstract
- We explore ultrafast charge transfer (CT) resonantly induced by hard X-ray radiation in organic thiophene-based polymers at the sulfur K-edge. A combination of core-hole clock spectroscopy with real-time propagation time-dependent density functional theory simulations gives an insight into the electron dynamics underlying the CT process. Our method provides control over CT by a selective excitation of a specific resonance in the sulfur atom with monochromatic X-ray radiation. Our combined experimental and theoretical investigation establishes that the dominant mechanism of CT in polymer powders and films consists of electron delocalisation along the polymer chain occurring on the low-femtosecond time scale.
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| 20. |
- Wallner, Måns, 1992, et al.
(författare)
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Coulomb Explosion of CD3I induced by single photon deep inner shell ionisation
- 2020
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- L-shell ionisation and subsequent coulomb explosion of fully deuterated methyl iodide, cD3i, irradiated with hard X-rays has been examined by a time-of-flight multi-ion coincidence technique. The core vacancies relax efficiently by Auger cascades, leading to charge states up to 16+. the dynamics of the Coulomb explosion process are investigated by calculating the ions’ flight times numerically based on a geometric model of the experimental apparatus, for comparison with the experimental data. A parametric model of the explosion, previously introduced for multi-photon induced coulomb explosion, is applied in numerical simulations, giving good agreement with the experimental results for medium charge states. Deviations for higher charges suggest the need to include nuclear motion in a putatively more complete model. Detection efficiency corrections from the simulations are used to determine the true distributions of molecular charge states produced by initial L1, L2 and L3 ionisation.
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