SwePub - sökning: WFRF:(Eland John H. D. 1941)

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1.	Sanchez-Gonzalez, A., et al. (författare) Auger electron and photoabsorption spectra of glycine in the vicinity of the oxygen K-edge measured with an X-FEL 2015 Ingår i: Journal of Physics B-Atomic Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 48:23 Tidskriftsartikel (refereegranskat)abstract We report the first measurement of the near oxygen K-edge auger spectrum of the glycine molecule. Our work employed an x-ray free electron laser as the photon source operated with input photon energies tunable between 527 and 547 eV. Complete electron spectra were recorded at each photon energy in the tuning range, revealing resonant and non-resonant auger structures. Finally ab initio theoretical predictions are compared with the measured above the edge auger spectrum and an assignment of auger decay channels is performed.
2.	Zhaunerchyk, Vitali, et al. (författare) Disentangling formation of multiple-core holes in aminophenol molecules exposed to bright X-FEL radiation 2015 Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 48:24 Tidskriftsartikel (refereegranskat)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).
3.	Mucke, Melanie, et al. (författare) Covariance mapping of two-photon double core hole states in C2H2 and C2H6 produced by an x-ray free electron laser 2015 Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 17 Tidskriftsartikel (refereegranskat)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.	Murphy, B. F., et al. (författare) Femtosecond X-ray-induced explosion of C-60 at extreme intensity 2014 Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 5 Tidskriftsartikel (refereegranskat)abstract Understanding molecular femtosecond dynamics under intense X-ray exposure is critical to progress in biomolecular imaging and matter under extreme conditions. Imaging viruses and proteins at an atomic spatial scale and on the time scale of atomic motion requires rigorous, quantitative understanding of dynamical effects of intense X-ray exposure. Here we present an experimental and theoretical study of C-60 molecules interacting with intense X-ray pulses from a free-electron laser, revealing the influence of processes not previously reported. Our work illustrates the successful use of classical mechanics to describe all moving particles in C-60, an approach that scales well to larger systems, for example, biomolecules. Comparisons of the model with experimental data on C-60 ion fragmentation show excellent agreement under a variety of laser conditions. The results indicate that this modelling is applicable for X-ray interactions with any extended system, even at higher X-ray dose rates expected with future light sources.
5.	Eland, John H. D., 1941, et al. (författare) Dissociation of multiply charged ICN by Coulomb explosion 2016 Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 145:7 Tidskriftsartikel (refereegranskat)abstract The fragmentations of iodine cyanide ions created with 2 to 8 positive charges by photoionization from inner shells with binding energies from 59 eV (I 4d) to ca. 900 eV (I 3p) have been examined by multi-electron and multi-ion coincidence spectroscopy with velocity map imaging ion capability. The charge distributions produced by hole formation in each shell are characterised and systematic effects of the number of charges and of initial charge localisation are found. Published by AIP Publishing.
6.	Feifel, Raimund, et al. (författare) Cationic double K-hole pre-edge states of CS2 and SF6 2017 Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 7 Tidskriftsartikel (refereegranskat)abstract Recent advances in X-ray instrumentation have made it possible to measure the spectra of an essentially unexplored class of electronic states associated with double inner-shell vacancies. Using the technique of single electron spectroscopy, spectra of states in CS2 and SF6 with a double hole in the K-shell and one electron exited to a normally unoccupied orbital have been obtained. The spectra are interpreted with the aid of a high-level theoretical model giving excellent agreement with the experiment. The results shed new light on the important distinction between direct and conjugate shake-up in a molecular context. In particular, systematic similarities and di erences between pre-edge states near single core holes investigated in X-ray absorption spectra and the corresponding states near double core holes studied here are brought out.
7.	Andersson, Jonas, et al. (författare) Auger decay of 4d inner-shell holes in atomic Hg leading to triple ionization 2017 Ingår i: Physical Review A. - : AMER PHYSICAL SOC. - 2469-9926 .- 2469-9934. ; 96 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.
8.	Andersson, Jonas, et al. (författare) Parametrization of energy sharing distributions in direct double photoionization of He 2019 Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 9 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.
9.	Andersson, Jonas, et al. (författare) Triple ionization of atomic Cd involving 4p(-1) and 4s(-1) inner-shell holes 2015 Ingår i: Physical Review A. - 1050-2947 .- 1094-1622. ; 92:2 Tidskriftsartikel (refereegranskat)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.
10.	Eland, John H. D., 1941, et al. (författare) Carbon dioxide ion dissociations after inner shell excitation and ionization: The origin of site-specific effects 2014 Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 140:18 Tidskriftsartikel (refereegranskat)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.
11.	Eland, John H. D., 1941, et al. (författare) Direct observation of three-electron collective decay in a resonant Auger process 2015 Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 17 Tidskriftsartikel (refereegranskat)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.
12.	Eland, John H. D., 1941, et al. (författare) Double and Triple Ionisation of Isocyanic Acid 2020 Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 10 Tidskriftsartikel (refereegranskat)abstract Double and triple ionisation spectra of the reactive molecule isocyanic acid (HNCO) have been measured using multi-electron and ion coincidence techniques combined with synchrotron radiation and compared with high-level theoretical calculations. Vertical double ionisation at an energy of 32.8±0.3eV forms the 3A” ground state in which the HNCO2+ ion is long lived. The vertical triple ionisation energy is determined as 65±1eV. The core-valence double ionisation spectra resemble the valence photoelectron spectrum in form, and their main features can be understood on the basis of a simple and rather widely applicable Coulomb model based on the characteristics of the molecular orbitals from which electrons are removed. Characteristics of the most important dissociation channels are examined and discussed.
13.	Eland, John H. D., 1941, et al. (författare) Double Photoionisation Spectra of Molecules 2017 Bok (övrigt vetenskapligt/konstnärligt)abstract This is the first ever compendium of double photoionisation spectra, covering some 70 of the most important small and medium sized molecules and thus providing an essential starting point for studies of the consequences of ionisation by high energy photons in both terrestrial and astrophysical environments. It also provides a complete non-mathematical description of all the phenomena and pathways involved in molecular double photoionisation. Most spectra are presented with identification of the electronic states and leading orbital configurations. The technique of magnetic bottle time-of-flight electron spectroscopy, used for all the spectra, is fully explained and compared with other techniques. For each molecule, the book gives full references to relevant work by complementary techniques and to theoretical calculations. Written in a clear non-mathematical style, this book is accessible to students as well as more experienced researchers. The authors have designed the layout for easy retrieval of any desired spectrum through the systematic organisation and ordering of the compounds and thorough indexing. As well as being a compendium of spectra, the book is a textbook covering all the known phenomenological aspects of molecular double photoionisation. The important phenomena are first mentioned in the introductory chapters, and are discussed in more detail in connection with the groups of molecules and individual cases where they are most relevant. The most useful spectra will be available in digital form for users.
14.	Eland, John H. D., 1941, et al. (författare) Ion charge-resolved branching in decay of inner shell holes in Xe up to 1200eV 2015 Ingår i: Journal of Physics B-Atomic Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 48:20 Tidskriftsartikel (refereegranskat)abstract Using a new multi-electron multi-ion coincidence apparatus and soft x-ray synchrotron radiation we have determined branching ratios to final Xen+ states with 2 < n < 9 from the 4d(-1), 4p(-1), 4s(-1), 3d(-1) and 3p(-1) Xe+ hole states. The coincident electron spectra give information on the Auger cascade pathways. We show that by judicious choice of coincident electrons, almost pure single charge states of the final ions can be selected.
15.	Eland, John H. D., 1941, et al. (författare) Triple ionisation of HCl via states with a 2p core hole 2019 Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 151 Tidskriftsartikel (refereegranskat)abstract The triple ionisation of HCl by double Auger decay and related processes has been studied using a multi-particle coincidence technique combined with synchrotron radiation. Four contributing processes are identified, direct double Auger, two indirect double Auger decay pathways and single Auger decay from core-valence doubly ionised intermediate states. One indirect Auger process involves autoionisation from superexcited states of Cl+. Double Auger decay from HCl+ (2p-1, 2PJ), which makes up 112% of total Auger decay, is estimated to be 40% direct, 15% indirect via atomic Cl+* and 45% indirect via molecular intermediate doubly ionized states. The vertical triple ionisation energy of HCl is determined as 73.80.5 eV. Molecular field effects are found to affect the direct double Auger process as well as normal single Auger decay. Comparison between spectra of the HCl and DCl isotopomers indicates that electronic decay is faster in all the processes than molecular dissociation.
16.	Eland, John H. D., 1941, et al. (författare) Wide range double photoionization spectra of N2 and CO2 2016 Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 646, s. 31-35 Tidskriftsartikel (refereegranskat)abstract Using a magnetic bottle time-of-flight electron spectrometer we have measured double photoionisation spectra of N2 and CO2 covering the range from threshold up to the triple ionisation energies. The experiments demonstrate the use of a new asynchronous chopper in eight-bunch mode of the synchrotron radiation source SOLEIL. For CO22+ some broad bands in the Auger spectra are found to have multiple resolved counterparts in the photoionisation spectrum. All the bands in the Auger spectra have counterparts in the photoionisation spectra, where extra bands attributed to triplet states are present. In the spectrum of N22+ we suggest reassignment of one band.
17.	Feifel, Raimund, et al. (författare) Ultrafast molecular three-electron Auger process 2016 Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 116 Tidskriftsartikel (refereegranskat)abstract Three-electron Auger decay is an exotic and elusive process, in which two outer-shell electrons simultaneously refill an inner-shell double vacancy with emission of a single Auger electron. Such transitions are forbidden by the many-electron selection rules, normally making their decay lifetimes orders of magnitude longer than the few-femtosecond lifetimes of normal (two-electron) Auger decay. Here we present theoretical predictions and direct experimental evidence for a few-femtosecond three-electron Auger decay of a double inner-valence-hole state in CH3F. Our analysis shows that in contrast to double core holes, double inner-valence vacancies in molecules can decay exclusively by this ultrafast three-electron Auger process, and we predict that this phenomenon occurs widely.
18.	Hedin, Lage, et al. (författare) Single site double core level ionisation of OCS 2014 Ingår i: Chemical Physics. - : Elsevier BV. - 0301-0104 .- 1873-4421. ; 439, s. 111-116 Tidskriftsartikel (refereegranskat)abstract Single site O1s, C1s and S2p double ionisation of the OCS molecule has been investigated using a magnetic bottle multi-electron coincidence time-of-flight spectrometer. Photon energies of 1300, 750 and 520 eV, respectively, were used for the ionisation, and spectra were obtained from which the double core ionisation energies could be determined. The energies measured for 1s double ionisation are 1172 eV (O1s(-2)) and 659 eV (C1s(-2)). For the S2p double ionisation three dicationic states are expected, P-3, D-1 and S-1. The ionisation energies obtained for these states are 373 eV (P-3), 380 eV (D-1) and 388 eV (S-1). The ratio between the double and single core ionisation energies are in all cases equal or close to 2.20. Auger spectra of OCS, associated with the O1s(-2), C1s(-2) and S2p(-2) dicationic states, were also recorded incorporating both electrons emitted as a result of the filling of the two core vacancies. As for other small molecules, the spectra show an atomic-like character with Auger bands located in the range 480-560 eV for oxygen, 235-295 eV for carbon and 100-160 eV for sulphur. The interpretation of the spectra is supported by CASSCF and CASCI calculations. The cross section ratio between double and single core hole creation was estimated as 3.7 x 10(-4) for oxygen at 1300 eV, 3.7 x 10(-4) for carbon at 750 eV and as 2.2 x 10(-3) for sulphur at 520 eV. (C) 2014 Elsevier B.V. All rights reserved.
19.	Hult Roos, Andreas, et al. (författare) Abundance of molecular triple ionization by double Auger decay 2018 Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 8 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.
20.	Hult Roos, Andreas, et al. (författare) Dissociations of water ions after valence and inner-valence ionization 2018 Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 149 Tidskriftsartikel (refereegranskat)abstract Energy selected and mass‐resolved electron‐ion coincidence spectra of heavy water have been recorded for ionization energies from 18 to 35 eV. Dissociation from the B2B2 state produces both O+ and D2+ at energies near their thermodynamic thresholds in addition to the known products D+ and OD+. Relative yields of O+, OD+ and D+ in the B2B2 state breakdown diagram are modulated by the vibrational structure of the B‐state population, implying incomplete energy equilibration before fragmentation. Decay from the C‐state produces OD+ in addition to the known O+ and D+. The fragment kinetic energies suggest that O+ and D+ from the C state are products of full atomization of the molecule.
21.	Hult Roos, Andreas, et al. (författare) Relative extent of double and single Auger decay in molecules containing C, N and O atoms 2016 Ingår i: Physical Chemistry Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 18:36, s. 25705-25710 Tidskriftsartikel (refereegranskat)abstract We show that the proportion of double Auger decay following creation of single 1s core holes in molecules containing C, N and O atoms is greater than usually assumed, amounting to about 10% of single Auger decay in many cases. It varies from molecule to molecule, where the size of the molecule has a positive correlation to the amount of double Auger decay. In neon, examined as a related benchmark, the proportion of double Auger decay is similar to that in methane, and is in the order of 5%.
22.	Hult Roos, Andreas, et al. (författare) Relative extent of triple Auger decay in CO and CO2 2019 Ingår i: Physical Chemistry Chemical Physics - PCCP. - 1463-9076. ; 21, s. 9889-94 Tidskriftsartikel (refereegranskat)abstract Systematic measurements on single and triple Auger decay in CO and CO2 after the creation of a C 1s or a O 1s core vacancy show that the percentage of triple Auger decay is on the order of 10−2 of the single Auger decay in these molecules. The fractions of triple Auger decay are compared with triple Auger fractions for carbon atoms and some noble gas atoms, and are found to follow a linear trend correlated to the number of valence electrons on the atom with the initial core vacancy and on its closest neighbours. This linear trend for the percentage of triple Auger decay is represented by a predictive equation TA = 0.13·Nve − 0.5.
23.	Hult Roos, Andreas, et al. (författare) Valence double ionization electron spectra of CH3F, CH3Cl and CH3I 2017 Ingår i: Chemical Physics. - : Elsevier BV. - 0301-0104 .- 1873-4421. ; 491, s. 42-47 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.
24.	Ideböhn, Veronica, 1992, et al. (författare) Symmetry breaking in core-valence double ionisation of allene 2023 Ingår i: Communications Chemistry. - : Springer Nature. - 2399-3669. ; 6:1 Tidskriftsartikel (refereegranskat)abstract Allene serves as a model to study multiple ionization of organic molecules. Here, the authors use synchrotron radiation-based multi-particle coincidence techniques and high-level ab initio calculations to propose a simple physical model to elucidate the symmetry breaking in core-valence double ionization of allene. Conventional electron spectroscopy is an established one-electron-at-the-time method for revealing the electronic structure and dynamics of either valence or inner shell ionized systems. By combining an electron-electron coincidence technique with the use of soft X-radiation we have measured a double ionisation spectrum of the allene molecule in which one electron is removed from a C1s core orbital and one from a valence orbital, well beyond Siegbahns Electron-Spectroscopy-for-Chemical-Analysis method. This core-valence double ionisation spectrum shows the effect of symmetry breaking in an extraordinary way, when the core electron is ejected from one of the two outer carbon atoms. To explain the spectrum we present a new theoretical approach combining the benefits of a full self-consistent field approach with those of perturbation methods and multi-configurational techniques, thus establishing a powerful tool to reveal molecular orbital symmetry breaking on such an organic molecule, going beyond Lowdins standard definition of electron correlation.
25.	Kolorenc, P., et al. (författare) Collective relaxation processes in atoms, molecules and clusters 2016 Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 49:8 Tidskriftsartikel (refereegranskat)abstract Electron correlation is an essential driver of a variety of relaxation processes in excited atomic and molecular systems. These are phenomena which often lead to autoionization typically involving two-electron transitions, such as the well-known Auger effect. However, electron correlation can give rise also to higher-order processes characterized by multi-electron transitions. Basic examples include simultaneous two-electron emission upon recombination of an inner-shell vacancy (double Auger decay) or collective decay of two holes with emission of a single electron. First reports of this class of processes date back to the 1960s, but their investigation intensified only recently with the advent of free-electron lasers. High fluxes of high-energy photons induce multiple excitation or ionization of a system on the femtosecond timescale and under such conditions the importance of multi-electron processes increases significantly. We present an overview of experimental and theoretical works on selected multi- electron relaxation phenomena in systems of different complexity, going from double Auger decay in atoms and small molecules to collective interatomic autoionization processes in nanoscale samples.
26.	Koulentianos, Dimitris, 1987, et al. (författare) Formation and relaxation of K-2 and K-2V double-core-hole states in n-butane 2022 Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 157:4 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.
27.	Salén, Peter, et al. (författare) Selectivity in fragmentation of N-methylacetamide after resonant K-shell excitation 2014 Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 16:29, s. 15231-15240 Tidskriftsartikel (refereegranskat)abstract The fragmentation pattern of the peptide model system, N-methylacetamide, is investigated using ion time-of-flight (TOF) spectroscopy after resonant K-shell excitation. Corresponding near-edge X-ray absorption fine structure (NEXAFS) spectra recorded at high resolution at the C1s, N1s and O1s edges are presented. Analysis of the ion TOF data reveals a multitude of fragmentation channels and dissociation pathways. Comparison between the excitation of six different resonances in the vicinity of the C1s, N1s and O1s edges suggests evidence for site-selective bond breaking. In particular the breaking of the peptide bond and the N-C-alpha bond show a clear correlation with resonant excitation at the N1s edge. Also, stronger tendencies towards site-selective bond breaking are found for the generation of single ions compared with ion pairs. Analysis of angular distributions of ions from breakage of the peptide bond yields a fragmentation time of <400 fs.
28.	Squibb, Richard J., et al. (författare) Acetylacetone photodynamics at a seeded free-electron laser 2018 Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 9 Tidskriftsartikel (refereegranskat)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.
29.	Valiev, Rashid R., et al. (författare) Optimization of core–valence states of molecules 2017 Ingår i: Molecular Physics. - : Taylor & Francis. - 0026-8976 .- 1362-3028. ; 115:1-2, s. 252-259 Tidskriftsartikel (refereegranskat)abstract Core–valence double-electron ionisation spectra of a few small molecules–carbon monoxide, ammonia, methyl fluoride and thiophene–are presented and analysed using the self-consistent field algorithm introduced by Hans Jørgen Jensen 30 years ago. It confirms the utility of this algorithm, frequently employed to obtain stable and sharp convergence of wave functions for the benefit of calculations of a great variety of molecular properties, thus also for optimisation of core–valence states and for the interpretation of the corresponding spectra.
30.	Wallner, Måns, 1992, et al. (författare) Abiotic molecular oxygen production—Ionic pathway from sulfur dioxide 2022 Ingår i: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 8:33 Tidskriftsartikel (refereegranskat)abstract Molecular oxygen, O2, is vital to life on Earth and possibly also on exoplanets. Although the biogenic processes leading to its accumulation in Earth’s atmosphere are well understood, its abiotic origin is still not fully established. Here, we report combined experimental and theoretical evidence for electronic state–selective production of O2 from SO2, a chemical constituent of many planetary atmospheres and one that played an important part on Earth in the Great Oxidation Event. The O2 production involves dissociative double ionization of SO2 leading to efficient formation of the O+2 O 2 + ion, which can be converted to abiotic O2 by electron neutralization or by charge exchange. This formation process may contribute substantially to the abundance of O2 and related ions in planetary atmospheres, such as the Jovian moons Io, Europa, and Ganymede. We suggest that this sort of ionic pathway for the formation of abiotic O2 involving multiply charged molecular ion decomposition may also exist for other atmospheric and planetary molecules.
31.	Wallner, Måns, 1992, et al. (författare) Coulomb Explosion of CD3I induced by single photon deep inner shell ionisation 2020 Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 10 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.
32.	Zagorodskikh, Sergey, et al. (författare) An experimental and theoretical study of core-valence double ionization of acetaldehyde (ethanal) 2016 Ingår i: Physical Chemistry Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 18:4, s. 2535-2547 Tidskriftsartikel (refereegranskat)abstract Core-valence double ionisation spectra of acetaldehyde (ethanal) are presented at photon energies above the carbon and oxygen 1s ionisation edges, measured by a versatile multi-electron coincidence spectroscopy technique. We use this molecule as a testbed for analyzing core-valence spectra by means of quantum chemical calculations of transition energies. These theoretical approaches range from two simple models, one based on orbital energies corrected by core valence interaction and one based on the equivalent core approximation, to a systematic series of quantum chemical electronic structure methods of increasing sophistication. The two simple models are found to provide a fast orbital interpretation of the spectra, in particular in the low energy parts, while the coverage of the full spectrum is best fulfilled by correlated models. CASPT2 is the most sophisticated model applied, but considering precision as well as computational costs, the single and double excitation configuration interaction model seems to provide the best option to analyze core-valence double hole spectra.
33.	Zagorodskikh, Sergey, et al. (författare) Mechanisms of site-specific photochemistry following core-shell ionization of chemically inequivalent carbon atoms in acetaldehyde (ethanal) 2016 Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 145:12 Tidskriftsartikel (refereegranskat)abstract Site-specific fragmentation upon 1s photoionisation of acetaldehyde has been studied using synchrotron radiation and a multi-electron-ion coincidence technique based on a magnetic bottle. Experimental evidence is presented that bond rupture occurs with highest probability in the vicinity of the initial charge localisation and possible mechanisms are discussed. We find that a significant contribution to site-specific photochemistry is made by different fragmentation patterns of individual quantum states populated at identical ionisation energies.
34.	Zhaunerchyk, Vitali, et al. (författare) Theory and simulations of covariance mapping in multiple dimensions for data analysis in high-event-rate experiments 2014 Ingår i: Physical Review A. - 1050-2947 .- 1094-1622. ; 89:5 Tidskriftsartikel (refereegranskat)abstract Multidimensional covariance analysis and its validity for correlation of processes leading to multiple products are investigated from a theoretical point of view. The need to correct for false correlations induced by experimental parameters which fluctuate from shot to shot, such as the intensity of self-amplified spontaneous emission x-ray free-electron laser pulses, is emphasized. Threefold covariance analysis based on simple extension of the two-variable formulation is shown to be valid for variables exhibiting Poisson statistics. In this case, false correlations arising from fluctuations in an unstable experimental parameter that scale linearly with signals can be eliminated by threefold partial covariance analysis, as defined here. Fourfold covariance based on the same simple extension is found to be invalid in general. Where fluctuations in an unstable parameter induce nonlinear signal variations, a technique of contingent covariance analysis is proposed here to suppress false correlations. In this paper we also show a method to eliminate false correlations associated with fluctuations of several unstable experimental parameters.

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