1. |
- Bueno, AM, et al.
(author)
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Influence of chemical bonds on the lifetime of the molecular-field-split 2p levels in H2S
- 2003
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In: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 67, s. 22714:1-7
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Journal article (peer-reviewed)abstract
- Different lifetime broadenings in molecular-field-split 2p core levels in H2S are predicted theoretically and are identified in an experimental investigation of the S 2p Auger electron spectrum. The measurements were performed for the transition to the vibrationally resolved X(1)A(1) ground state of H2S2+. The lifetimes of the 3e(1/2) and 5e(1/2) levels of the 2p ionized molecule are found to be 64 and 74 meV, respectively. This unambiguous determination of the lifetime difference of 10+/-1 meV is only possible as the 4e(1/2)-->X(1)A(1)(2b(1)(-2)) decay channel that overlaps the 5e(1/2)-->X(1)A(1)(2b(1)(-2)) channel is practically suppressed in Auger decay in H2S. The lifetime difference is confirmed by ab initio calculations. A theoretical analysis shows that it results from the mutual orientation of the core hole in the intermediate states and the valence electron density in the sulfur 3p orbitals. Both are strongly influenced by the chemical bond. Thus the observed effect is the direct result of a fundamental property of molecular electronic structure.
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2. |
- Eland, John H. D., et al.
(author)
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Single and multiple photoionisation of H(2)S by 40-250 eV photons
- 2011
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In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 13:41, s. 18428-18435
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Journal article (peer-reviewed)abstract
- Multi-electron coincidence measurements on photoionisation of H(2)S have been carried out at photon energies from 40 to 250 eV. They quantify molecular field effects on the Auger process in detail and are in good agreement with the existing theory. Spectra of core-valence double ionisation of H(2)S are presented and partially analysed. Auger decays from the core-valence states produce triply charged product spectra with unexplained and surprising intensity distributions. Triple ionisation by the double Auger process from 2p hole states shows little effect of the molecular field splitting, but includes a substantial contribution from cascade processes, some involving dissociation in intermediate states. The onset of triple ionisation at the molecular geometry is determined as 61 +/- 0.5 eV.
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3. |
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4. |
- Andersson, Egil, 1981-, et al.
(author)
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Core-valence double photoionization of the CS2 molecule
- 2010
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 133:9, s. 94305-
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Journal article (peer-reviewed)abstract
- Double photoionization spectra of the CS2 molecule have been recorded using the TOF-PEPECO technique in combination with synchrotron radiation at the photon energies h nu=220, 230, 240, 243, and 362.7 eV. The spectra were recorded in the S 2p and C 1s inner-shell ionization regions and reflect dicationic states formed out of one inner-shell vacancy and one vacancy in the valence region. MCSCF calculations were performed to model the energies of the dicationic states. The spectra associated with a S 2p vacancy are well structured and have been interpreted in some detail by comparison to conventional S 2p and valence photoelectron spectra. The lowest inner-shell-valence dicationic state is observed at the vertical double ionization energy 188.45 eV and is associated with a (2p(3/2))(-1)(2 pi(g))(-1) double vacancy. The spectrum connected to the C 1s vacancy shows a distinct line at 310.8 eV, accompanied by additional broad features at higher double ionization energies. This line is associated with a (C 1s)(-1)(2 pi(g))(-1) double vacancy. (C-) 2010 American Institute of Physics. [doi: 10.1063/1.3469812]
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5. |
- Andersson, E., et al.
(author)
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Formation of Kr3+ via core-valence doubly ionized intermediate states
- 2012
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In: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 85:3, s. 032502-
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Journal article (peer-reviewed)abstract
- The time-of-flight photoelectron-photoion coincidence technique has been used to study single-photon 3d(9)4p(5) core-valence double ionization of Kr and subsequent Auger decay to triply charged states associated with the 4s(2)4p(3) and 4s(1)4p(4) configurations. The photon energy used was h nu = 150 eV. Multiconfiguration Dirac-Fock calculations were performed both for the doubly ionized intermediate states and the triply ionized final states. The intermediate states of Kr2+ are observed between 120 and 125 eV, whereas the final states of Kr3+ are observed between 74- and 120-eV ionization energy. Assignments of all structures are made based on the present numerical results. The calculated Auger rates give a detailed explanation of the relative line strengths observed.
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6. |
- Andersson, Egil, 1981-
(author)
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Multi-Electron Coincidence Studies of Atoms and Molecules
- 2010
-
Doctoral thesis (other academic/artistic)abstract
- This thesis concerns multi-ionization coincidence measurements of atoms and small molecules using a magnetic bottle time-of-flight (TOF) spectrometer designed for multi-electron coincidence studies. Also, a time-of-flight mass spectrometer has been used together with the TOF electron spectrometer for electron-ion coincidence measurements. The multi-ionization processes have been studied by employing a pulsed discharge lamp in the vacuum ultraviolet spectral region and synchrotron radiation in the soft X-ray region. The designs of the spectrometers are described in some detail, and several timing schemes suitable for the light sources mentioned above are presented.Studies have been performed on krypton, molecular oxygen, carbon disulfide and a series of alcohol molecules. For the latter, double ionization spectra have been recorded and new information has been obtained on the dicationic states. A recently found rule-of-thumb and quantum chemical calculations have been used to quantify the effective distance of the two vacancies in the dications of these molecules.For Kr, O2, and CS2, single-photon core-valence spectra have been obtained at the synchrotron radiation facility BESSY II in Berlin and interpreted on the basis of quantum chemical calculations. These spectra show a remarkable similarity to conventional valence photoelectron spectra.Spectra of triply charged ions were recorded, also at BESSY II, for Kr and CS2 by measuring, in coincidence, all three electrons ejected. The complex transition channels leading to tricationic states were mapped in substantial detail for Kr. It was found that for 3d-ionized krypton, the tricationic states are dominantly populated by cascade Auger decays via distinct intermediate states whose energies have been determined. The triple ionization spectra of CS2 from the direct double Auger effect via S2p, S2s and C1s hole states contain several resolved features and show selectivity based on the initial charge localisation and on the identity of the initial state.
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7. |
- Andersson, Egil, 1981-, et al.
(author)
-
Multielectron coincidence study of the double Auger decay of 3d-ionized krypton
- 2010
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In: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 82:4, s. 043418-
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Journal article (peer-reviewed)abstract
- Multielectron coincidence data for triple ionization of krypton have been recorded above the 3d ionization threshold at two photon energies (140 and 150 eV). Three principal transition pathways have been observed, two involving double Auger transitions from Kr+, and one involving single Auger transitions from Kr2+ created by direct single-photon double ionization. The decay of the 3d(9) D-2(5/2,3/2) states in Kr+ has been analyzed in some detail and is found to be strongly dominated by cascade processes where two electrons with well-defined energies are emitted. The decay paths leading to the 4s(2)4p(3) S-4, D-2, and P-2 states of Kr3+ are analyzed and energies of seven intermediate states in Kr2+ are given. A preliminary investigation of the decay paths from Kr+ 3d (9)4p(5)nl shake-up states has also been carried out.
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8. |
- Andersson, Jonas, et al.
(author)
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Auger decay of 4d inner-shell holes in atomic Hg leading to triple ionization
- 2017
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In: Physical Review A. - : AMER PHYSICAL SOC. - 2469-9926 .- 2469-9934. ; 96
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Journal article (peer-reviewed)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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9. |
- Andersson, Jonas, et al.
(author)
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Parametrization of energy sharing distributions in direct double photoionization of He
- 2019
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In: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 9
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Journal article (peer-reviewed)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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10. |
- Andersson, Jonas, et al.
(author)
-
Triple ionization of atomic Cd involving 4p(-1) and 4s(-1) inner-shell holes
- 2015
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In: Physical Review A. - 1050-2947 .- 1094-1622. ; 92:2
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Journal article (peer-reviewed)abstract
- The triple ionization spectrum of atomic Cd formed upon the removal of a 4p or a 4s inner-shell electron and subsequent Auger decays has been obtained at 200 eV photon energy. By using a versatile multielectron coincidence detection technique based on a magnetic bottle spectrometer in combination with multiconfiguration Dirac-Fock calculations, Auger cascades leading to tricationic final states have been analyzed and final-state configurations have been identified. The most prominent Auger cascades leading to the ground state of Cd3+ have been identified in good agreement with theory.
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11. |
- Asmussen, J. D., et al.
(author)
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Time-Resolved Ultrafast Interatomic Coulombic Decay in Superexcited Sodium-Doped Helium Nanodroplets
- 2022
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In: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 13:20, s. 4470-4478
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Journal article (peer-reviewed)abstract
- The autoionization dynamics of super excited superfluid He nanodropletsdoped with Na atoms is studied by extreme-ultraviolet (XUV) time-resolved electronspectroscopy. Following excitation into the higher-lying droplet absorption band, the dropletrelaxes into the lowest metastable atomic 1s2s1,3Sstates from which interatomic Coulombicdecay (ICD) takes place either between two excited He atoms or between an excited He atomand a Na atom attached to the droplet surface. Four main ICD channels are identified, andtheir decay times are determined by varying the delay between the XUV pulse and a UV pulsethat ionizes the initial excited state and thereby quenches ICD. The decay times for thedifferent channels all fall in the range of similar to 1 ps, indicating that the ICD dynamics are mainlydetermined by the droplet environment. A periodic modulation of the transient ICD signals istentatively attributed to the oscillation of the bubble forming around the localized Heexcitation
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12. |
- Asmussen, J. D., et al.
(author)
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Unravelling the full relaxation dynamics of superexcited helium nanodroplets
- 2021
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In: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 23:28, s. 15138-15149
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Journal article (peer-reviewed)abstract
- The relaxation dynamics of superexcited superfluid He nanodroplets is thoroughly investigated by means of extreme-ultraviolet (XUV) femtosecond electron and ion spectroscopy complemented by time-dependent density functional theory (TDDFT). Three main paths leading to the emission of electrons and ions are identified: droplet autoionization, pump-probe photoionization, and autoionization induced by re-excitation of droplets relaxing into levels below the droplet ionization threshold. The most abundant product ions are He-2(+), generated by droplet autoionization and by photoionization of droplet-bound excited He atoms. He+ appear with some pump-probe delay as a result of the ejection He atoms in their lowest excited states from the droplets. The state-resolved time-dependent photoelectron spectra reveal that intermediate excited states of the droplets are populated in the course of the relaxation, terminating in the lowest-lying metastable singlet and triplet He atomic states. The slightly faster relaxation of the triplet state compared to the singlet state is in agreement with the simulation showing faster formation of a bubble around a He atom in the triplet state.
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13. |
- Barillot, T., et al.
(author)
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Correlation-Driven Transient Hole Dynamics Resolved in Space and Time in the Isopropanol Molecule
- 2021
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In: Physical Review X. - : American Physical Society. - 2160-3308. ; 11:3
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Journal article (peer-reviewed)abstract
- The possibility of suddenly ionized molecules undergoing extremely fast electron hole (or hole) dynamics prior to significant structural change was first recognized more than 20 years ago and termed charge migration. The accurate probing of ultrafast electron hole dynamics requires measurements that have both sufficient temporal resolution and can detect the localization of a specific hole within the molecule. We report an investigation of the dynamics of inner valence hole states in isopropanol where we use an x-ray pump-x-ray probe experiment, with site and state-specific probing of a transient hole state localized near the oxygen atom in the molecule, together with an ab initio theoretical treatment. We record the signature of transient hole dynamics and make the first tentative observation of dynamics driven by frustrated Auger-Meitner transitions. We verify that the effective hole lifetime is consistent with our theoretical prediction. This state-specific measurement paves the way to widespread application for observations of transient hole dynamics localized in space and time in molecules and thus to charge transfer phenomena that are fundamental in chemical and material physics.
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14. |
- Berrah, Nora, et al.
(author)
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Double-core-hole spectroscopy for chemical analysis with an intense X-ray femtosecond laser
- 2011
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In: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 108:41, s. 16912-16915
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Journal article (peer-reviewed)abstract
- Theory predicts that double-core-hole (DCH) spectroscopy can provide a new powerful means of differentiating between similar chemical systems with a sensitivity not hitherto possible. Although DCH ionization on a single site in molecules was recently measured with double-and single-photon absorption, double-core holes with single vacancies on two different sites, allowing unambiguous chemical analysis, have remained elusive. Here we report that direct observation of double-core holes with single vacancies on two different sites produced via sequential two-photon absorption, using short, intense X-ray pulses from the Linac Coherent Light Source free-electron laser and compare it with theoretical modeling. The observation of DCH states, which exhibit a unique signature, and agreement with theory proves the feasibility of the method. Our findings exploit the ultrashort pulse duration of the free-electron laser to eject two core electrons on a time scale comparable to that of Auger decay and demonstrate possible future X-ray control of physical inner-shell processes.
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15. |
- Berrah, N., et al.
(author)
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Femtosecond-resolved observation of the fragmentation of buckminsterfullerene following X-ray multiphoton ionization
- 2019
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In: Nature Physics. - : Springer Science and Business Media LLC. - 1745-2473 .- 1745-2481. ; 15, s. 1279-1283
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Journal article (peer-reviewed)abstract
- X-ray free-electron lasers have, over the past decade, opened up the possibility of understanding the ultrafast response of matter to intense X-ray pulses. In earlier research on atoms and small molecules, new aspects of this response were uncovered, such as rapid sequences of inner-shell photoionization and Auger ionization. Here, we studied a larger molecule, buckminsterfullerene (C60), exposed to 640eV X-rays, and examined the role of chemical effects, such as chemical bonds and charge transfer, on the fragmentation following multiple ionization of the molecule. To provide time resolution, we performed femtosecond-resolved X-ray pump/X-ray probe measurements, which were accompanied by advanced simulations. The simulations and experiment reveal that despite substantial ionization induced by the ultrashort (20fs) X-ray pump pulse, the fragmentation of C60 is considerably delayed. This work uncovers the persistence of the molecular structure of C60, which hinders fragmentation over a timescale of hundreds of femtoseconds. Furthermore, we demonstrate that a substantial fraction of the ejected fragments are neutral carbon atoms. These findings provide insights into X-ray free-electron laser-induced radiation damage in large molecules, including biomolecules.
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16. |
- Berrah, Nora, et al.
(author)
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Femtosecond x-ray induced fragmentation of fullerenes
- 2016
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In: Journal of Modern Optics. - : Informa UK Limited. - 0950-0340 .- 1362-3044. ; 63:4, s. 390-401
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Journal article (peer-reviewed)abstract
- A new class of femtosecond, intense, short – wavelength lasers – the free-electron laser – has opened up new opportunities to investigate the structure and dynamics in many scientific areas. These new lasers, whose performance keeps increasing, enable the understanding of physical and chemical changes at an atomic spatial scale and on the time scale of atomic motion which is essential for a broad range of scientific fields. We describe here the interaction of fullerenes in the multiphoton regime with the Linac Coherent Light Source (LCLS) X-ray free-electron laser at SLAC National Laboratory. In particular, we report on new data regarding the ionization of Ho3N@C80 molecules and compare the results with our prior C60 investigation of radiation damage induced by the LCLS pulses. We also discuss briefly the potential impact of newly available instrumentation to physical and chemical sciences when they are coupled with FELs as well as theoretical calculations and modeling.
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17. |
- Bolognesi, P., et al.
(author)
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A study of the dynamical energy flow in uracil
- 2015
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In: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 635
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Journal article (peer-reviewed)abstract
- The time resolved photoionization of C 1s in uracil following excitation of the neutral molecule by 260 nm pulses has been studied at LCLS.
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18. |
- Borne, Kurtis D., et al.
(author)
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Ultrafast electronic relaxation pathways of the molecular photoswitch quadricyclane
- 2024
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In: NATURE CHEMISTRY. - : Springer Nature. - 1755-4330 .- 1755-4349. ; 16, s. 499-505
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Journal article (peer-reviewed)abstract
- The light-induced ultrafast switching between molecular isomers norbornadiene and quadricyclane can reversibly store and release a substantial amount of chemical energy. Prior work observed signatures of ultrafast molecular dynamics in both isomers upon ultraviolet excitation but could not follow the electronic relaxation all the way back to the ground state experimentally. Here we study the electronic relaxation of quadricyclane after exciting in the ultraviolet (201 nanometres) using time-resolved gas-phase extreme ultraviolet photoelectron spectroscopy combined with non-adiabatic molecular dynamics simulations. We identify two competing pathways by which electronically excited quadricyclane molecules relax to the electronic ground state. The fast pathway (<100 femtoseconds) is distinguished by effective coupling to valence electronic states, while the slow pathway involves initial motions across Rydberg states and takes several hundred femtoseconds. Both pathways facilitate interconversion between the two isomers, albeit on different timescales, and we predict that the branching ratio of norbornadiene/quadricyclane products immediately after returning to the electronic ground state is approximately 3:2.
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19. |
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20. |
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21. |
- Busto, David, et al.
(author)
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Probing electronic decoherence with high-resolution attosecond photoelectron interferometry
- 2022
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In: European Physical Journal D. - : Springer Science and Business Media LLC. - 1434-6060 .- 1434-6079. ; 76:7
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Journal article (peer-reviewed)abstract
- Abstract: Quantum coherence plays a fundamental role in the study and control of ultrafast dynamics in matter. In the case of photoionization, entanglement of the photoelectron with the ion is a well-known source of decoherence when only one of the particles is measured. Here, we investigate decoherence due to entanglement of the radial and angular degrees of freedom of the photoelectron. We study two-photon ionization via the 2s2p autoionizing state in He using high spectral resolution photoelectron interferometry. Combining experiment and theory, we show that the strong dipole coupling of the 2s2p and 2p2 states results in the entanglement of the angular and radial degrees of freedom. This translates, in angle-integrated measurements, into a dynamic loss of coherence during autoionization. Graphic Abstract: [Figure not available: see fulltext.]. © 2022, The Author(s).
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22. |
- Busto, D., et al.
(author)
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Time-frequency representation of autoionization dynamics in helium
- 2018
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In: Journal of Physics B-Atomic Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 51:4
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Journal article (peer-reviewed)abstract
- Autoionization, which results from the interference between direct photoionization and photoexcitation to a discrete state decaying to the continuum by configuration interaction, is a well known example of the important role of electron correlation in light-matter interaction. Information on this process can be obtained by studying the spectral, or equivalently, temporal complex amplitude of the ionized electron wave packet. Using an energy-resolved interferometric technique, we measure the spectral amplitude and phase of autoionized wave packets emitted via the sp2+ and sp3(+) resonances in helium. These measurements allow us to reconstruct the corresponding temporal profiles by Fourier transform. In addition, applying various time-frequency representations, we observe the build-up of the wave packets in the continuum, monitor the instantaneous frequencies emitted at any time and disentangle the dynamics of the direct and resonant ionization channels.
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23. |
- Ehara, M., et al.
(author)
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Symmetry and vibrationally resolved absorption spectra near the N K edges of N2O : experiment and theory
- 2011
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In: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 83:6, s. 062506-
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Journal article (peer-reviewed)abstract
- In this study, angle-resolved energetic-ion yield spectra were measured in the N 1s excitation region of N2O. A Franck-Condon analysis based on ab initio two-dimensional potential energy surfaces of the core-excited Rydberg states, which were calculated by the symmetry-adapted cluster-configuration interaction method, reproduced observed vibrational excitations specific to the individual Rydberg states well and enabled quantitative assignments. Geometric changes in the terminal nitrogen N-t 1s and the central nitrogen N-c 1s excited states with respect to the 3p pi, 3p sigma, and 4s sigma transitions were analyzed. The coupling of these valence and Rydbergs states was examined based on the second moment analysis. Irregular Rydberg-state behavior in the N-c 1s(-1) 4s sigma state was observed.
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24. |
- Eland, John H. D., 1941, et al.
(author)
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Carbon dioxide ion dissociations after inner shell excitation and ionization: The origin of site-specific effects
- 2014
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 140:18
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Journal article (peer-reviewed)abstract
- Multi-coincidence experiments with detection of both electrons and ions from decay of core-excited and core-ionized states of CO2 confirm that O-2(+) is formed specifically in Auger decay from the C1s-pi* and O1s-pi* resonances. Molecular rearrangement occurs by bending in the resonant states, and O-2(+) is produced by both single and double Auger decay. It is suggested that electron capture by C+ after partial dissociation in the doubly ionized core of excited CO2+, formed by shake-up in spectator resonant Auger decay, accounts for high kinetic energy and high internal energy in some C + O-2(+) fragments. (C) 2014 AIP Publishing LLC.
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25. |
- Eland, John H. D., 1941, et al.
(author)
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Direct observation of three-electron collective decay in a resonant Auger process
- 2015
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In: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 17
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Journal article (peer-reviewed)abstract
- Using a multi-electron coincidence technique combined with synchrotron radiation we demonstrate the real existence of the elusive three-electron collective process in resonant Auger decay of Kr. The three-electron process is about 40 times weaker than the competing two-electron processes.
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