| 41. |
- Brasse, Felix, et al.
(author)
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Time-resolved inner-shell photoelectron spectroscopy : From a bound molecule to an isolated atom
- 2018
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In: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - 2469-9926 .- 2469-9934. ; 97:4
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Journal article (peer-reviewed)abstract
- Due to its element and site specificity, inner-shell photoelectron spectroscopy is a widely used technique to probe the chemical structure of matter. Here, we show that time-resolved inner-shell photoelectron spectroscopy can be employed to observe ultrafast chemical reactions and the electronic response to the nuclear motion with high sensitivity. The ultraviolet dissociation of iodomethane (CH3I) is investigated by ionization above the iodine 4d edge, using time-resolved inner-shell photoelectron and photoion spectroscopy. The dynamics observed in the photoelectron spectra appear earlier and are faster than those seen in the iodine fragments. The experimental results are interpreted using crystal-field and spin-orbit configuration interaction calculations, and demonstrate that time-resolved inner-shell photoelectron spectroscopy is a powerful tool to directly track ultrafast structural and electronic transformations in gas-phase molecules.
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| 42. |
- Burt, Michael, et al.
(author)
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Coulomb-explosion imaging of concurrent CH2BrI photodissociation dynamics
- 2017
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In: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - 2469-9926 .- 2469-9934. ; 96:4
-
Journal article (peer-reviewed)abstract
- The dynamics following laser-induced molecular photodissociation of gas-phase CH2BrI at 271.6 nm were investigated by time-resolved Coulomb-explosion imaging using intense near-IR femtosecond laser pulses. The observed delay-dependent photofragment momenta reveal that CH2BrI undergoes C-I cleavage, depositing 65.6% of the available energy into internal product states, and that absorption of a second UV photon breaks the C-Br bond of C(H)2Br. Simulations confirm that this mechanism is consistent with previous data recorded at 248 nm, demonstrating the sensitivity of Coulomb-explosion imaging as a real-time probe of chemical dynamics.
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| 43. |
- Cheng, Yu Chen, et al.
(author)
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Imaging multiphoton ionization dynamics of CH3I at a high repetition rate XUV free-electron laser
- 2021
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In: Journal of Physics B-Atomic Molecular and Optical Physics. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 54:1
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Journal article (peer-reviewed)abstract
- XUV multiphoton ionization of molecules is commonly used in free-electron laser experiments to study charge transfer dynamics. However, molecular dissociation and electron dynamics, such as multiple photon absorption, Auger decay, and charge transfer, often happen on competing time scales, and the contributions of individual processes can be difficult to unravel. We experimentally investigate the Coulomb explosion dynamics of methyl iodide upon core-hole ionization of the shallow inner-shell of iodine (4d) and classically simulate the fragmentation by phenomenologically introducing ionization dynamics and charge transfer. Under our experimental conditions with medium fluence and relatively long XUV pulses (similar to 75 fs), we find that fast Auger decay prior to charge transfer significantly contributes to the charging mechanism, leading to a yield enhancement of higher carbon charge states upon molecular dissociation. Furthermore, we argue for the existence of another charging mechanism for the weak fragmentation channels leading to triply charged carbon atoms. This study shows that classical simulations can be a useful tool to guide the quantum mechanical description of the femtosecond dynamics upon multiphoton absorption in molecular systems.
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| 44. |
- de Zwarte, Sonja M. C., et al.
(author)
-
The association between familial risk and brain abnormalities is disease specific : an ENIGMA-relatives study of schizophrenia and bipolar disorder
- 2019
-
In: Biological Psychiatry. - : Elsevier. - 0006-3223 .- 1873-2402. ; 86:7, s. 545-556
-
Journal article (peer-reviewed)abstract
- BACKGROUND: Schizophrenia and bipolar disorder share genetic liability, and some structural brain abnormalities are common to both conditions. First-degree relatives of patients with schizophrenia (FDRs-SZ) show similar brain abnormalities to patients, albeit with smaller effect sizes. Imaging findings in first-degree relatives of patients with bipolar disorder (FDRs-BD) have been inconsistent in the past, but recent studies report regionally greater volumes compared with control subjects.METHODS: We performed a meta-analysis of global and subcortical brain measures of 6008 individuals (1228 FDRs-SZ, 852 FDRs-BD, 2246 control subjects, 1016 patients with schizophrenia, 666 patients with bipolar disorder) from 34 schizophrenia and/or bipolar disorder family cohorts with standardized methods. Analyses were repeated with a correction for intracranial volume (ICV) and for the presence of any psychopathology in the relatives and control subjects.RESULTS: FDRs-BD had significantly larger ICV (d = +0.16, q < .05 corrected), whereas FDRs-SZ showed smaller thalamic volumes than control subjects (d = -0.12, q < .05 corrected). ICV explained the enlargements in the brain measures in FDRs-BD. In FDRs-SZ, after correction for ICV, total brain, cortical gray matter, cerebral white matter, cerebellar gray and white matter, and thalamus volumes were significantly smaller; the cortex was thinner (d < -0.09, q < .05 corrected); and third ventricle was larger (d = +0.15, q < .05 corrected). The findings were not explained by psychopathology in the relatives or control subjects.CONCLUSIONS: Despite shared genetic liability, FDRs-SZ and FDRs-BD show a differential pattern of structural brain abnormalities, specifically a divergent effect in ICV. This may imply that the neurodevelopmental trajectories leading to brain anomalies in schizophrenia or bipolar disorder are distinct.
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| 45. |
- Kockert, Hansjochen, et al.
(author)
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UV-induced dissociation of CH2BrI probed by intense femtosecond XUV pulses
- 2022
-
In: JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 55:1
-
Journal article (peer-reviewed)abstract
- The ultraviolet (UV)-induced dissociation and photofragmentation of gas-phase CH2BrI molecules induced by intense femtosecond extreme ultraviolet (XUV) pulses at three different photon energies are studied by multi-mass ion imaging. Using a UV-pump-XUV-probe scheme, charge transfer between highly charged iodine ions and neutral CH2Br radicals produced by C-I bond cleavage is investigated. In earlier charge-transfer studies, the center of mass of the molecules was located along the axis of the bond cleaved by the pump pulse. In the present case of CH2BrI, this is not the case, thus inducing a rotation of the fragment. We discuss the influence of the rotation on the charge transfer process using a classical over-the-barrier model. Our modeling suggests that, despite the fact that the dissociation is slower due to the rotational excitation, the critical interatomic distance for charge transfer is reached faster. Furthermore, we suggest that charge transfer during molecular fragmentation may be modulated in a complex way.
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| 46. |
- Pathak, S., et al.
(author)
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Tracking the ultraviolet-induced photochemistry of thiophenone during and after ultrafast ring opening
- 2020
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In: Nature Chemistry. - : Springer Science and Business Media LLC. - 1755-4330 .- 1755-4349. ; 12:9, s. 795-800
-
Journal article (peer-reviewed)abstract
- Photoinduced isomerization reactions lie at the heart of many chemical processes in nature. The mechanisms of such reactions are determined by a delicate interplay of coupled electronic and nuclear dynamics occurring on the femtosecond scale, followed by the slower redistribution of energy into different vibrational degrees of freedom. Here we apply time-resolved photoelectron spectroscopy with a seeded extreme ultraviolet free-electron laser to trace the ultrafast ring opening of gas-phase thiophenone molecules following ultraviolet photoexcitation. When combined with ab initio electronic structure and molecular dynamics calculations of the excited- and ground-state molecules, the results provide insights into both the electronic and nuclear dynamics of this fundamental class of reactions. The initial ring opening and non-adiabatic coupling to the electronic ground state are shown to be driven by ballistic S-C bond extension and to be complete within 350 fs. Theory and experiment also enable visualization of the rich ground-state dynamics that involve the formation of, and interconversion between, ring-opened isomers and the cyclic structure, as well as fragmentation over much longer timescales.
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| 47. |
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| 48. |
- Stern, S., et al.
(author)
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Toward atomic resolution diffractive imaging of isolated molecules with X-ray free-electron lasers
- 2014
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In: Faraday Discussions. - : Royal Society of Chemistry (RSC). - 1364-5498. ; 171, s. 393-418
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Journal article (peer-reviewed)abstract
- We give a detailed account of the theoretical analysis and the experimental results of an X-ray-diffraction experiment on quantum-state selected and strongly laser-aligned gasphase ensembles of the prototypical large asymmetric rotor molecule 2,5-diiodobenzonitrile, performed at the Linac Coherent Light Source [Phys. Rev. Lett. 112, 083002 (2014)]. This experiment is the first step toward coherent diffractive imaging of structures and structural dynamics of isolated molecules at atomic resolution, i.e., picometers and femtoseconds, using X-ray free-electron lasers.
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| 49. |
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| 50. |
- Aquila, Andrew, et al.
(author)
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Time-resolved protein nanocrystallography using an X-ray free-electron laser
- 2012
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In: Optics Express. - 1094-4087. ; 20:3, s. 2706-2716
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Journal article (peer-reviewed)abstract
- We demonstrate the use of an X-ray free electron laser synchronized with an optical pump laser to obtain X-ray diffraction snapshots from the photoactivated states of large membrane protein complexes in the form of nanocrystals flowing in a liquid jet. Light-induced changes of Photosystem I-Ferredoxin co-crystals were observed at time delays of 5 to 10 µs after excitation. The result correlates with the microsecond kinetics of electron transfer from Photosystem I to ferredoxin. The undocking process that follows the electron transfer leads to large rearrangements in the crystals that will terminally lead to the disintegration of the crystals. We describe the experimental setup and obtain the first time-resolved femtosecond serial X-ray crystallography results from an irreversible photo-chemical reaction at the Linac Coherent Light Source. This technique opens the door to time-resolved structural studies of reaction dynamics in biological systems.
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