SwePub - search: WFRF:(Piancastelli Maria N.)

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1.	Jahnke, T., et al. (author) Inner-Shell-Ionization-Induced Femtosecond Structural Dynamics of Water Molecules Imaged at an X-Ray Free-Electron Laser 2021 In: Physical Review X. - : American Physical Society. - 2160-3308. ; 11:4 Journal article (peer-reviewed)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.	Frasinski, L. J., et al. (author) Dynamics of Hollow Atom Formation in Intense X-Ray Pulses Probed by Partial Covariance Mapping 2013 In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 111:7, s. 073002- Journal article (peer-reviewed)abstract When exposed to ultraintense x-radiation sources such as free electron lasers (FELs) the innermost electronic shell can efficiently be emptied, creating a transient hollow atom or molecule. Understanding the femtosecond dynamics of such systems is fundamental to achieving atomic resolution in flash diffraction imaging of noncrystallized complex biological samples. We demonstrate the capacity of a correlation method called partial covariance mapping'' to probe the electron dynamics of neon atoms exposed to intense 8 fs pulses of 1062 eV photons. A complete picture of ionization processes competing in hollow atom formation and decay is visualized with unprecedented ease and the map reveals hitherto unobserved nonlinear sequences of photoionization and Auger events. The technique is particularly well suited to the high counting rate inherent in FEL experiments.
3.	Mucke, Melanie, et al. (author) Covariance mapping of two-photon double core hole states in C2H2 and C2H6 produced by an x-ray free electron laser 2015 In: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 17 Journal article (peer-reviewed)abstract Few-photon ionization and relaxation processes in acetylene (C2H2) and ethane (C2H6) were investigated at the linac coherent light source x-ray free electron laser (FEL) at SLAC, Stanford using a highly efficient multi-particle correlation spectroscopy technique based on a magnetic bottle. The analysis method of covariance mapping has been applied and enhanced, allowing us to identify electron pairs associated with double core hole (DCH) production and competing multiple ionization processes including Auger decay sequences. The experimental technique and the analysis procedure are discussed in the light of earlier investigations of DCH studies carried out at the same FEL and at third generation synchrotron radiation sources. In particular, we demonstrate the capability of the covariance mapping technique to disentangle the formation of molecular DCH states which is barely feasible with conventional electron spectroscopy methods.
4.	Squibb, Richard J., et al. (author) Acetylacetone photodynamics at a seeded free-electron laser 2018 In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 9 Journal article (peer-reviewed)abstract Thefirst steps in photochemical processes, such as photosynthesis or animal vision, involvechanges in electronic and geometric structure on extremely short time scales. Time-resolvedphotoelectron spectroscopy is a natural way to measure such changes, but has been hinderedhitherto by limitations of available pulsed light sources in the vacuum-ultraviolet and soft X-ray spectral region, which have insufficient resolution in time and energy simultaneously. Theunique combination of intensity, energy resolution, and femtosecond pulse duration of theFERMI-seeded free-electron laser can now provide exceptionally detailed information onphotoexcitation–deexcitation and fragmentation in pump-probe experiments on the 50-femtosecond time scale. For the prototypical system acetylacetone we report here electronspectra measured as a function of time delay with enough spectral and time resolution tofollow several photoexcited species through well-characterized individual steps, interpretedusing state-of-the-art static and dynamics calculations. These results open the way forinvestigations of photochemical processes in unprecedented detail.
5.	Zhaunerchyk, Vitali, et al. (author) Disentangling formation of multiple-core holes in aminophenol molecules exposed to bright X-FEL radiation 2015 In: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 48:24 Journal article (peer-reviewed)abstract Competing multi-photon ionization processes, some leading to the formation of double core hole states, have been examined in 4-aminophenol. The experiments used the linac coherent light source (LCLS) x-ray free electron laser, in combination with a time-of-flight magnetic bottle electron spectrometer and the correlation analysis method of covariance mapping. The results imply that 4-aminophenol molecules exposed to the focused x-ray pulses of the LCLS sequentially absorb more than two x-ray photons, resulting in the formation of multiple core holes as well as in the sequential removal of photoelectrons and Auger electrons (so-called PAPA sequences).
6.	Zhaunerchyk, Vitali, et al. (author) Using covariance mapping to investigate the dynamics of multi-photon ionization processes of Ne atoms exposed to X-FEL pulses 2013 In: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 46:16, s. 164034- Journal article (peer-reviewed)abstract We report on a detailed investigation into the electron emission processes of Ne atoms exposed to intense femtosecond x-ray pulses, provided by the Linac Coherent Light Source Free Electron Laser (FEL) at Stanford. The covariance mapping technique is applied to analyse the data, and the capability of this approach to disentangle both linear and nonlinear correlation features which may be hidden on coincidence maps of the same data set is demonstrated. Different correction techniques which enable improvements on the quality of the spectral features extracted from the covariance maps are explored. Finally, a method for deriving characteristics of the x-ray FEL pulses based on covariance mapping in combination with model simulations is presented.
7.	Berrah, Nora, et al. (author) Double-core-hole spectroscopy for chemical analysis with an intense X-ray femtosecond laser 2011 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 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.
8.	Bolognesi, P., et al. (author) A study of the dynamical energy flow in uracil 2015 In: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 635 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.
9.	Bomme, C., et al. (author) Post-collision interaction manifestation in molecular systems probed by photoelectron-molecular ion coincidences 2013 In: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 46:21, s. 215101- Journal article (peer-reviewed)abstract S1s photoionization in carbonyl sulfide (OCS), followed by multiple Auger decay is investigated both experimentally and theoretically, by means of photoelectron-ion coincidences. A strong influence of post-collision interaction is observed in the energy shift and the distortion of the photoelectron spectra. The magnitude of this effect depends on the total charge of the ionic fragments, i.e., on the number of electrons emitted during the decay of the inner vacancy. A satisfactory agreement is found between experiment and theory, which allows us to estimate the lifetimes of the various two-hole states of the intermediate OCS2+ ion.
10.	Boudjemia, N., et al. (author) Deep-core photoionization of krypton atoms below and above the 1s ionization threshold 2020 In: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : AMER PHYSICAL SOC. - 2469-9926 .- 2469-9934. ; 101:5 Journal article (peer-reviewed)abstract Electronic relaxation of atomic Kr below and above the 1s ionization threshold is investigated experimentally using hard x-ray photoelectron spectroscopy. The experimental results are interpreted with the aid of relativistic Dirac-Fock calculations. The 1s orbital core-hole lifetime is extracted and the satellite's structures accompanying the photoelectron main line are assigned. Auger spectra recorded below and above the K edge are also investigated. In particular, the Auger cascade originating from vacancies of different origin in the L shell is analyzed in great detail. Competition between radiative KL versus nonradiative KLL Auger emission is emphasized.
11.	Boudjemia, N., et al. (author) Electron spectroscopy and dynamics of HBr around the Br 1s(-1) threshold 2020 In: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 22:46, s. 26806-26818 Journal article (peer-reviewed)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.
12.	Boudjemia, N., et al. (author) Experimental and theoretical study of the Kr L-shell Auger decay 2021 In: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : American Physical Society. - 2469-9926 .- 2469-9934. ; 104:1 Journal article (peer-reviewed)abstract The LMM Auger spectra of krypton are measured using the photon energies hv = 1709 eV, 1792 eV, 1950 eV, and 13 keV. This approach allows separating the contributions from the various core holes L-1 , L-2., and L-3. Previously unobserved transitions are presented. Complementary theoretical work is performed allowing the assignment of the spectral features. The L2,3Y -MMY (Y = M-4,M-5, N-1,N-2,N-3) Auger transitions of Kr2+ formed via Coster-Kronig Auger decay of the core holes L-1 and L-2. are also investigated. These spectra comprise about 4000 and 13 000 transitions, respectively, so that only general statements on the assignment, such as the configurations involved in the transitions, can be given.
13.	Ceolin, Denis, et al. (author) Site-selective resonant Auger spectroscopy of iso-dichloroethylene at the carbon K-edge 2012 In: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 185:8-9, s. 252-258 Journal article (peer-reviewed)abstract This study focuses on the two C1s-to-LUMO (lowest unoccupied molecular orbital) excitations of the iso-dichloroethylene (H2C=CCl2) and the subsequent Auger decay. We investigate the effect of the two different carbon core excitations on the population of the cation produced after electronic relaxation. The resonant Auger spectra are interpreted by comparison to the valence shells photoionization spectrum and with the help of theoretical calculations. Several consequences of the core-hole localization on the electronic decay are observed. In particular, the resonant excitation of the C1s(CH2) to the LUMO leads to a large intensity increase in the region of the first satellite state, whereas no dramatic changes are observed for the C1s(CCl2) excitation.
14.	Goldsztejn, G., et al. (author) Double-Core-Hole States in Neon: Lifetime, Post-Collision Interaction, and Spectral Assignment 2016 In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 117:13 Journal article (peer-reviewed)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.
15.	Guillemin, R., et al. (author) Selecting core-hole localization or delocalization in CS2 by photofragmentation dynamics 2015 In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 6 Journal article (peer-reviewed)abstract Electronic core levels in molecules are highly localized around one atomic site. However, in single-photon ionization of symmetric molecules, the question of core-hole localization versus delocalization over two equivalent atoms has long been debated as the answer lies at the heart of quantum mechanics. Here, using a joint experimental and theoretical study of core-ionized carbon disulfide (CS2), we demonstrate that it is possible to experimentally select distinct molecular-fragmentation pathways in which the core hole can be considered as either localized on one sulfur atom or delocalized between two indistinguishable sulfur atoms. This feat is accomplished by measuring photoelectron angular distributions within the frame of the molecule, directly probing entanglement or disentanglement of quantum pathways as a function of how the molecule dissociates.
16.	Larsson, Mats, et al. (author) Double core-hole formation in small molecules at the LCLS free electron laser 2013 In: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 46:16, s. 164030- Journal article (peer-reviewed)abstract We have investigated nonlinear processes in small molecules by x-ray photoelectron spectroscopy using the Linac Coherent Light Source free electron laser, and by simulations. The main focus of the experiments was the formation of the two-site double core-hole (tsDCH) states in the molecules CO2, N2O and N-2. These experiments are described in detail and the results are compared with simulations of the photoelectron spectra. The double core-hole states, and in particular the tsDCH states, have been predicted to be highly sensitive to the chemical environment. The theory behind this chemical sensitivity is validated by the experiments. Furthermore, our simulations of the relative integrated intensities of the peaks associated with the nonlinear processes show that this type of simulation, in combination with experimental data, provides a useful tool for estimating the duration of ultra-short x-ray pulses.
17.	Marchenko, T., et al. (author) Potential Energy Surface Reconstruction and Lifetime Determination of Molecular Double-Core-Hole States in the Hard X-Ray Regime 2017 In: Physical Review Letters. - : AMER PHYSICAL SOC. - 0031-9007 .- 1079-7114. ; 119:13 Journal article (peer-reviewed)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.
18.	Sahlén, Martin, et al. (author) Experimental Verification of the Chemical Sensitivity of Two-Site Double Core-Hole States Formed by an X-Ray Free-Electron Laser 2012 In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 108:15, s. 153003- Journal article (peer-reviewed)abstract We have performed x-ray two-photon photoelectron spectroscopy using the Linac Coherent Light Source x-ray free-electron laser in order to study double core-hole (DCH) states of CO2, N2O, and N-2. The experiment verifies the theory behind the chemical sensitivity of two-site DCH states by comparing a set of small molecules with respect to the energy shift of the two-site DCH state and by extracting the relevant parameters from this shift.
19.	Santos, A. C. F., et al. (author) Resonant Auger decay induced by the symmetry-forbidden 1a(1g)? 6a(1g) transition of the SF6 molecule 2022 In: Journal of Vacuum Science & Technology A. - : American Vacuum Society. - 0734-2101 .- 1520-8559. ; 40:4 Journal article (peer-reviewed)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.
20.	Stolte, W. C., et al. (author) Inner-shell photofragmentation of Cl-2 2010 In: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 43:15, s. 155202- Journal article (peer-reviewed)abstract We report an extensive study on partial-ion-yield spectroscopy around the Cl 1s and 2p ionization thresholds for Cl-2. All positive ion channels, several with the same mass/charge ratio, which could be distinguished by taking the advantage of the Cl-37 isotope, have been measured at a photon resolution of nearly 6500. At the Cl 1s ionization threshold, no significant differences are reported between the absorption and the partial-ion yields. In contrast, near the 2p ionization thresholds, we detect large variations in the fragmentation patterns following excitations to the Rydberg series when comparing the atomic fragment ions to the molecular fragment ions. We attribute the different behaviours to the more-or-less diffuse nature of Rydberg states with different angular momenta.
21.	Travnikova, Oksana, et al. (author) Selective vibrational excitation in the resonant Auger decay following core-to-pi transitions in N2O 2010 In: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 181:2-3, s. 129-134 Journal article (peer-reviewed)abstract In N2O a detailed study of the vibrational distribution of the (X) over tilde state reached after decay of core-to-pi* excitation of N terminal, N central and 0 1s core levels is reported. We observe a change in the relative intensity of bending versus stretching modes while scanning the photon energy across all three resonances. While this effect is known to be due to the Renner-Teller splitting in the core-excited states, we could derive that the antisymmetric stretching is excited mainly in the decay of the N terminal 1s-to-pi* excitation. An explanation for such selectivity is provided in terms of interplay of vibrational structure on potential energy surfaces of different electronic states involved in the process.
22.	Travnikova, O., et al. (author) Subfemtosecond Control of Molecular Fragmentation by Hard X-Ray Photons 2017 In: Physical Review Letters. - : AMER PHYSICAL SOC. - 0031-9007 .- 1079-7114. ; 118:21 Journal article (peer-reviewed)abstract Tuning hard x-ray excitation energy along Cl 1s -> sigma* resonance in gaseous HCl allows manipulating molecular fragmentation in the course of the induced multistep ultrafast dissociation. The observations are supported by theoretical modeling, which shows a strong interplay between the topology of the potential energy curves, involved in the Auger cascades, and the so-called core-hole clock, which determines the time spent by the system in the very first step. The asymmetric profile of the fragmentation ratios reflects different dynamics of nuclear wave packets dependent on the photon energy.
23.	Ueda, Kiyoshi, et al. (author) Roadmap on photonic, electronic and atomic collision physics : I. Light-matter interaction 2019 In: Journal of Physics B. - : IOP PUBLISHING LTD. - 0953-4075 .- 1361-6455. ; 52:17 Journal article (peer-reviewed)abstract We publish three Roadmaps on photonic, electronic and atomic collision physics in order to celebrate the 60th anniversary of the ICPEAC conference. In Roadmap I, we focus on the light-matter interaction. In this area, studies of ultrafast electronic and molecular dynamics have been rapidly growing, with the advent of new light sources such as attosecond lasers and x-ray free electron lasers. In parallel, experiments with established synchrotron radiation sources and femtosecond lasers using cutting-edge detection schemes are revealing new scientific insights that have never been exploited. Relevant theories are also being rapidly developed. Target samples for photon-impact experiments are expanding from atoms and small molecules to complex systems such as biomolecules, fullerene, clusters and solids. This Roadmap aims to look back along the road, explaining the development of these fields, and look forward, collecting contributions from twenty leading groups from the field.

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