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09/2011; , ISBN: 9780470749593
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ABSTRACT: Dissociative nuclear motion in core-excited molecular states leads to a splitting of the fragment Auger lines: the Auger-Doppler effect. We present here for the first time experimental evidence for an Auger-Doppler effect following F1s → a(1g)* inner-shell excitation by circularly polarized x rays in SF(6). In spite of a uniform distribution of the dissociating S-F bonds near the polarization plane of the light, the intersection between the subpopulation of molecules selected by the core excitation with the cone of dissociation induces a strong anisotropy in the distribution of the S-F bonds that contributes to the scattering profile measured in the polarization plane.
Physical Review Letters 12/2010; 105(23):233001. · 7.37 Impact Factor
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ABSTRACT: Based on angularly and vibrationally resolved electron spectroscopy measurements in acetylene, we report the first observation of anomalously strong vibrational anisotropy of resonant Auger scattering through the C 1s→π* excited state. We provide a theoretical model explaining the new phenomenon by three coexisting interference effects: (i) interference between resonant and direct photoionization channels, (ii) interference of the scattering channels through the core-excited bending states with orthogonal orientation of the molecular orbitals, (iii) scattering through two wells of the double-well bending mode potential. The interplay of nuclear and electronic motions offers in this case a new type of nuclear wave packet interferometry sensitive to the anisotropy of nuclear dynamics: whether which-path information is available or not depends on the final vibrational state serving for path selection.
Physical Review Letters 08/2010; 105(9):093002. · 7.37 Impact Factor
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Ji-Cai Liu,
Christophe Nicolas,
Yu-Ping Sun,
Roberto Flammini,
Patrick O'Keeffe,
Lorenzo Avaldi,
Paul Morin,
Victor Kimberg,
Nobuhiro Kosugi,
Faris Gel'mukhanov, Catalin Miron
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ABSTRACT: Resonant Auger spectra of ethene molecule have been measured with vibrational resolution at several excitation energies in the region of the C1s(-1)1b(2g)(π*) resonance. The main features observed in the experiment have been assigned and are accurately interpreted on the basis of ab initio multimode calculations. Theory explains the extended vibrational distribution of the resonant Auger spectra and its evolution as a function of the excitation energy by multimode excitation during the scattering process. As a result, the resonant Auger spectra display two qualitatively different spectral features following the Raman and non-Raman dispersion laws, respectively. Calculations show that two observed thresholds of formation of non-Raman spectral bands are related to the "double-edge" structure of the X-ray absorption spectrum.
The Journal of Physical Chemistry B 07/2010; 115(18):5103-12. · 3.70 Impact Factor
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ABSTRACT: Core excitation triggers nuclear dynamics on the femtosecond time scale. A multiparametric electron/ion coincidence approach has been used to disentangle complex decay processes occurring at short (molecular) or long (atomic) time scales. Methyl chloride has been excited by scanning along the dissociative Cl2p-->sigma* resonance. The detailed chronology of the competing decay processes, leading to either the rearrangement product HCl(+), or an ultrafast dissociation leading to Cl(+), has been investigated. The observed Auger-Doppler shift has been analyzed for various orientations of the electron and fragment ion.
The Journal of Chemical Physics 04/2008; 128(15):154314. · 3.33 Impact Factor
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ABSTRACT: A core-excited sulfur state with a lifetime almost one order of magnitude longer than in molecular 2p core-hole states is selectively produced by ultrafast dissociation of S 2p → σ* excited OCS. Clear evidence for this is provided by strong atomic peaks (20% of the total intensity) in x-ray fluorescence but very weak ones (2%) in the corresponding resonant Auger spectrum. Corroborating the assignment of the spectra, ab initio calculations explain the enhanced lifetime: the Auger decay of the produced 3D3 (2p53p5) sulfur state is strongly decreased as it contradicts a newly derived propensity rule of the L2,3MM Auger decay.
Journal of Physics B Atomic Molecular and Optical Physics 06/2006; 39(12):L269. · 1.88 Impact Factor
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Alexandra Mocellin,
Karoline Wiesner,
Stacey L. Sorensen, Catalin Miron,
Karine Le Guen,
Denis Céolin,
Marc Simon,
Paul Morin,
André Bueno Machado,
Olle Björneholm,
Arnaldo Naves de Brito
Chemical Physics Letters 435:214-218. · 2.34 Impact Factor
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ABSTRACT: Electron analysis combined with ion mass spectrometry is shown to be a unique tool to understand fragmentation dynamics of core-excited molecules. This article describes in detail a new setup devoted to energy and angle correlations measurements between the emitted particles resulting from inner-shell ionization or excitation. The data collection system is based on a pair of position sensitive detectors mounted behind a double toroidal electron analyzer and a short time-of-flight ion spectrometer. Because all relevant information results in time measurements, a natural synchronization in the events recording is obtained. The optimized geometry for the ion extraction allows spatial focusing for the ion trajectories by means of inhomogeneous extraction fields while preserving the time focusing. The N2 molecule has been used for full characterization of the setup whereas the CO2 molecule illustrates the role of the intermediate resonant state in controlling the final dissociation pattern. The bending mode excitation is shown to emphasize the O+ production, and the ion kinetic energy distribution is rationalized through an impulsive model.
Journal of Electron Spectroscopy and Related Phenomena 141:171-181. · 1.96 Impact Factor
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ABSTRACT: The present review article gives a historical overview of high-resolution inner-shell coincidence spectroscopies followed by selected examples showing their scientific impact in studying molecular fragmentation dynamics. The development of such spectroscopies was intimately related to the last 20 years spectacular advances of the instrumentation. They include the construction of high-performance soft X-ray beamlines at the newest synchrotron radiation facilities, but also the remarkable improvement of charged particles analyzers and detectors and the extensive use of multidimensional coincidence techniques allowing for simultaneous recording and further correlation of several physical parameters. From the examples shown, it clearly appears the importance of using coincidence measurements in addition to pure electron spectroscopy methods in order to fully characterize the complex decay processes of inner-shell excited species leading for instance to site-selective fragmentation, vibrational motion mediated dissociation or ultrafast intramolecular recombination processes. The perspectives of the field will be briefly drawn in the end.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment.
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