| 1. |
- 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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| 2. |
- Fang, L., et al.
(author)
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Multiple Ionization and Double Core-hole Production in Molecules using the LCLS X-ray FEL
- 2012
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In: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 388:3, s. 032028-
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Journal article (peer-reviewed)abstract
- We used the world's first hard x-ray FEL to investigate the response of molecular systems to the ultra-intense, femtosecond x-ray radiation. We report sequential multiphoton ionization, frustrated absorption and double core hole production mechanisms.
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| 3. |
- Frasinski, L. J., et al.
(author)
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Dynamics of Hollow Atom Formation in Intense X-Ray Pulses Probed by Partial Covariance Mapping
- 2013
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 111:7, s. 073002-
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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.
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| 4. |
- Larsson, Mats, et al.
(author)
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Double core-hole formation in small molecules at the LCLS free electron laser
- 2013
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In: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 46:16, s. 164030-
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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.
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| 5. |
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| 6. |
- McFarland, B. K., et al.
(author)
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Ultrafast X-ray Auger probing of photoexcited molecular dynamics
- 2014
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In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 5, s. 4235-
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Journal article (peer-reviewed)abstract
- Molecules can efficiently and selectively convert light energy into other degrees of freedom. Disentangling the underlying ultrafast motion of electrons and nuclei of the photoexcited molecule presents a challenge to current spectroscopic approaches. Here we explore the photoexcited dynamics of molecules by an interaction with an ultrafast X-ray pulse creating a highly localized core hole that decays via Auger emission. We discover that the Auger spectrum as a function of photoexcitation-X-ray-probe delay contains valuable information about the nuclear and electronic degrees of freedom from an element-specific point of view. For the nucleobase thymine, the oxygen Auger spectrum shifts towards high kinetic energies, resulting from a particular C-O bond stretch in the pi pi* photoexcited state. A subsequent shift of the Auger spectrum towards lower kinetic energies displays the electronic relaxation of the initial photoexcited state within 200 fs. Ab-initio simulations reinforce our interpretation and indicate an electronic decay to the n pi* state.
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| 7. |
- Mucke, Melanie, et al.
(author)
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Covariance mapping of two-photon double core hole states in C2H2 and C2H6 produced by an x-ray free electron laser
- 2015
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In: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 17
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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.
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| 8. |
- 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
-
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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| 9. |
- Sahlén, Martin, et al.
(author)
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Experimental Verification of the Chemical Sensitivity of Two-Site Double Core-Hole States Formed by an X-Ray Free-Electron Laser
- 2012
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 108:15, s. 153003-
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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.
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| 10. |
- Saleacuten, P., et al.
(author)
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X-ray FEL-induced Double Core-Hole Formation in Polyatomic Molecules
- 2012
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In: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 388:2, s. 022083-
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Journal article (peer-reviewed)abstract
- We use extremely intense, ultrashort soft X-Ray pulses generated by the LCLS X-Ray Free Electron Laser to investigate the production of molecular double core-hole states by sequential two-photon X-Ray absorption. The effect of critical LCLS parameters such as the number of photons per pulse, the pulse duration, and the focal spot size on the photoelectron and Auger spectra is modeled in detail and the results of these simulations are used as an aid in the interpretation of the experimental spectra obtained. The emphasis is on double core-hole formation in small polyatomic molecules such as CO2.
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