| 1. |
- Jahnke, T., et al.
(författare)
-
Inner-Shell-Ionization-Induced Femtosecond Structural Dynamics of Water Molecules Imaged at an X-Ray Free-Electron Laser
- 2021
-
Ingår i: Physical Review X. - : American Physical Society. - 2160-3308. ; 11:4
-
Tidskriftsartikel (refereegranskat)abstract
- The ultrafast structural dynamics of water following inner-shell ionization is a crucial issue in high-energy radiation chemistry. We have exposed isolated water molecules to a short x-ray pulse from a free-electron laser and detected momenta of all produced ions in coincidence. By combining experimental results and theoretical modeling, we can image dissociation dynamics of individual molecules in unprecedented detail. We reveal significant molecular structural dynamics in H2O2+, such as asymmetric deformation and bond-angle opening, leading to two-body or three-body fragmentation on a timescale of a few femtoseconds. We thus reconstruct several snapshots of structural dynamics at different time intervals, which highlight dynamical patterns that are relevant as initiating steps of subsequent radiation-damage processes.
|
|
| 2. |
- 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.
|
|
| 3. |
- Carniato, S., et al.
(författare)
-
Thomson-resonant interference effects in elastic x-ray scattering near the Cl K edge of HCl
- 2012
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 137:9, s. 094311-
-
Tidskriftsartikel (refereegranskat)abstract
- We experimentally observed interference effects in elastic x-ray scattering from gas-phase HCl in the vicinity of the Cl Kedge. Comparison to theory identifies these effects as interference effects between non-resonant elastic Thomson scattering and resonant Raman scattering. The results indicate the non-resonant Thomson and resonant Raman contributions are of comparable strength. The measurements also exhibit strong polarization dependence, allowing an easy identification of the resonant and non-resonant contributions.
|
|
| 4. |
- Guillemin, R., et al.
(författare)
-
Photoelectron-Auger-electron angular-momentum transfer in core-ionized Ar : Beyond the standard post-collision-interaction model
- 2019
-
Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : AMER PHYSICAL SOC. - 2469-9926 .- 2469-9934. ; 99:6
-
Tidskriftsartikel (refereegranskat)abstract
- Electron-ion coincidence experimental data obtained following argon 1s photoionization are reported. Slow photoelectrons were measured in coincidence with Ar+ and Ar2+ ions, and the beta angular distribution parameter was obtained. The measured beta parameter for the Ar2+-photoelectron coincidence measurements shows a significant deviation from the beta = 2 expected value. With the support of a quantum mechanical theory of post-collision interaction (PCI) which goes beyond the standard model, we attribute this deviation to angular-momentum exchange due to the interaction of the photoelectron with the Auger electron, while the role of the residual ion is negligible. The main mechanism of angular-momentum transfer and its effect on the asymmetry parameter beta near the photoionization threshold are considered.
|
|
| 5. |
- 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.
|
|
| 6. |
- 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.
|
|
| 7. |
- 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.
|
|
| 8. |
- 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.
|
|
| 9. |
- 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.
|
|
| 10. |
- 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.
|
|
