| 1. |
- Frasinski, L. J., et al.
(författare)
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Dynamics of Hollow Atom Formation in Intense X-Ray Pulses Probed by Partial Covariance Mapping
- 2013
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 111:7, s. 073002-
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Tidskriftsartikel (refereegranskat)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.
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| 2. |
- Zhaunerchyk, Vitali, et al.
(författare)
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Using covariance mapping to investigate the dynamics of multi-photon ionization processes of Ne atoms exposed to X-FEL pulses
- 2013
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 46:16, s. 164034-
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Tidskriftsartikel (refereegranskat)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.
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| 3. |
- Murphy, B. F., et al.
(författare)
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Femtosecond X-ray-induced explosion of C-60 at extreme intensity
- 2014
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 5
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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.
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| 4. |
- Eland, John H. D., 1941, et al.
(författare)
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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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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 140:18
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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.
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| 5. |
- Linusson, Per, et al.
(författare)
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Complete double valence photoionization study of the electron spectra of krypton
- 2013
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 88:2, s. 022510-
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Tidskriftsartikel (refereegranskat)abstract
- Double photoionization spectra of Kr have been recorded using monochromatized synchrotron radiation of 88 eV photon energy and a versatile multielectron coincidence time-of-flight spectroscopy technique. The formation of the Kr2+ states of the lowest-energy configuration 4s(2)4p(4) is partly direct, producing electron pairs with a continuous distribution, and partly indirect via superexcited singly ionized states. The superexcited Kr+ states show strong and hitherto unexplained selectivity in branching to final Kr2+ states. Kr2+ states based on excited configurations are formed mainly by direct double photoionization.
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| 6. |
- Salén, Peter, et al.
(författare)
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Selectivity in fragmentation of N-methylacetamide after resonant K-shell excitation
- 2014
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 16:29, s. 15231-15240
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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.
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