| 1. |
- Murphy, B. F., et al.
(author)
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Femtosecond X-ray-induced explosion of C-60 at extreme intensity
- 2014
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In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 5
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Journal article (peer-reviewed)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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| 2. |
- 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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| 3. |
- Hedin, Lage, et al.
(author)
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Single site double core level ionisation of OCS
- 2014
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In: Chemical Physics. - : Elsevier BV. - 0301-0104 .- 1873-4421. ; 439, s. 111-116
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Journal article (peer-reviewed)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.
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| 4. |
- Salén, Peter, et al.
(author)
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Selectivity in fragmentation of N-methylacetamide after resonant K-shell excitation
- 2014
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In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 16:29, s. 15231-15240
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Journal article (peer-reviewed)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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| 5. |
- Zhaunerchyk, Vitali, et al.
(author)
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Theory and simulations of covariance mapping in multiple dimensions for data analysis in high-event-rate experiments
- 2014
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In: Physical Review A. - 1050-2947 .- 1094-1622. ; 89:5
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Journal article (peer-reviewed)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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