| 1. |
- Bennett, Kochise, et al.
(författare)
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Multidimensional resonant nonlinear spectroscopy with coherent broadband x-ray pulses
- 2016
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Ingår i: Physica Scripta. - : IOP PUBLISHING LTD. - 0031-8949 .- 1402-4896. ; T169
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Tidskriftsartikel (refereegranskat)abstract
- New x-ray free electron laser (XFEL) and high harmonic generation (HHG) light sources are capable of generating short and intense pulses that make x-ray nonlinear spectroscopy possible. Multidimensional spectroscopic techniques, which have long been used in the nuclear magnetic resonance, infrared, and optical regimes to probe the electronic structure and nuclear dynamics of molecules by sequences of short pulses with variable delays, can thus be extended to the attosecond x-ray regime. This opens up the possibility of probing core-electronic structure and couplings, the real-time tracking of impulsively created valence-electronic wavepackets and electronic coherences, and monitoring ultrafast processes such as nonadiabatic electron-nuclear dynamics near conical-intersection crossings. We survey various possible types of multidimensional x-ray spectroscopy techniques and demonstrate the novel information they can provide about molecules.
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| 2. |
- Cho, Daeheum, et al.
(författare)
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Imaging of transition charge densities involving carbon core excitations by all X-ray sum-frequency generation
- 2019
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Ingår i: Philosophical Transactions. Series A. - : The Royal Society. - 1364-503X .- 1471-2962. ; 377:2145
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Tidskriftsartikel (refereegranskat)abstract
- X-ray diffraction signals from the time-evolving molecular charge density induced by selective core excitation of chemically inequivalent carbon atoms are calculated. A narrowband X-ray pulse selectively excites the carbon K-edge of the –CH3 or –CH2F groups in fluoroethane (CH3–CH2F). Each excitation creates a distinct core coherence which depends on the character of the electronic transition. Direct propagation of the reduced single-electron density matrix, using real-time time-dependent density functional theory, provides the time-evolving charge density following interactions with external fields. The interplay between partially filled valence molecular orbitals upon core excitation induces characteristic femtosecond charge migration which depends on the core–valence coherence, and is monitored by the sum-frequency generation diffraction signal.
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| 3. |
- Hua, Weijie, et al.
(författare)
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Study of double core hole excitations in molecules by X-ray double-quantum-coherence signals : a multi-configuration simulation
- 2016
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Ingår i: Chemical Science. - : Royal Society of Chemistry. - 2041-6520 .- 2041-6539. ; 7:9, s. 5922-5933
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Tidskriftsartikel (refereegranskat)abstract
- The multi-configurational self-consistent field method is employed to simulate the two-dimensional all-X-ray double-quantum-coherence (XDQC) spectroscopy, a four-wave mixing signal that provides direct signatures of double core hole (DCH) states. The valence electronic structure is probed by capturing the correlation between the single (SCH) and double core hole states. The state-averaged restricted-activespace self-consistent field (SA-RASSCF) approach is used which can treat the valence, SCH, and DCH states at the same theoretical level, and applies to all types of DCHs (located on one or two atoms, K-edge or L-edge), with both accuracy and efficiency. Orbital relaxation introduced by the core hole(s) and the static electron correlation is properly accounted for. The XDQC process can take place via different intermediate DCH state channels by tuning the pulse frequencies. We simulate the XDQC signals for the three isomers of aminophenol at 8 pulse frequency configurations, covering all DCH pathways involving the N1s and O1s core hole (N1sN1s, O1sO1s and N1sO1s), which reveal different patterns of valence excitations.
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| 4. |
- Kowalewski, Markus, 1980-, et al.
(författare)
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Monitoring nonadiabatic dynamics in molecules by ultrafast X-Ray diffraction
- 2019
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Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2100-014X. ; 205
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Tidskriftsartikel (refereegranskat)abstract
- We theoretically examine time-resolved diffraction from molecules which undergo non-adiabatic dynamics and identify contributions from inelastic scattering that indicate the presence of an avoided crossing and the corresponding nuclear configuration.
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| 5. |
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| 6. |
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| 7. |
- Osipov, Vladimir Al., et al.
(författare)
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Multiscale wavelet decomposition of time-resolved X-ray diffraction signals in cyclohexadiene
- 2018
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 115:41, s. 10269-10274
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate how the wavelet transform, which is a powerful tool for compression, filtering, and scaling analysis of signals, may be used to separate large- and short-scale electron density features in X-ray diffraction patterns. Wavelets can isolate the electron density associated with delocalized bonds from the much stronger background of highly localized core electrons. The wavelet-processed signals clearly reveal the bond formation and breaking in the early steps of the photoinduced pericyclic ring opening reaction of 1,3-cyclohexadiene, which are not resolved in the bare signal.
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| 8. |
- Young, Linda, et al.
(författare)
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Roadmap of ultrafast x-ray atomic and molecular physics
- 2018
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 51:3
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Forskningsöversikt (refereegranskat)abstract
- X-ray free-electron lasers (XFELs) and table-top sources of x-rays based upon high harmonic generation (HHG) have revolutionized the field of ultrafast x-ray atomic and molecular physics, largely due to an explosive growth in capabilities in the past decade. XFELs now provide unprecedented intensity (1020 W cm-2) of x-rays at wavelengths down to ∼1 Ångstrom, and HHG provides unprecedented time resolution (∼50 attoseconds) and a correspondingly large coherent bandwidth at longer wavelengths. For context, timescales can be referenced to the Bohr orbital period in hydrogen atom of 150 attoseconds and the hydrogen-molecule vibrational period of 8 femtoseconds; wavelength scales can be referenced to the chemically significant carbon K-edge at a photon energy of ∼280 eV (44 Ångstroms) and the bond length in methane of ∼1 Ångstrom. With these modern x-ray sources one now has the ability to focus on individual atoms, even when embedded in a complex molecule, and view electronic and nuclear motion on their intrinsic scales (attoseconds and Ångstroms). These sources have enabled coherent diffractive imaging, where one can image non-crystalline objects in three dimensions on ultrafast timescales, potentially with atomic resolution. The unprecedented intensity available with XFELs has opened new fields of multiphoton and nonlinear x-ray physics where behavior of matter under extreme conditions can be explored. The unprecedented time resolution and pulse synchronization provided by HHG sources has kindled fundamental investigations of time delays in photoionization, charge migration in molecules, and dynamics near conical intersections that are foundational to AMO physics and chemistry. This roadmap coincides with the year when three new XFEL facilities, operating at Ångstrom wavelengths, opened for users (European XFEL, Swiss-FEL and PAL-FEL in Korea) almost doubling the present worldwide number of XFELs, and documents the remarkable progress in HHG capabilities since its discovery roughly 30 years ago, showcasing experiments in AMO physics and other applications. Here we capture the perspectives of 17 leading groups and organize the contributions into four categories: ultrafast molecular dynamics, multidimensional x-ray spectroscopies; high-intensity x-ray phenomena; attosecond x-ray science.
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