| 1. |
- Céolin, A, et al.
(författare)
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Study of the Dissociation of Nitrous Oxide Following Resonant Excitation of the Nitrogen and Oxygen K-shells
- 2008
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 128:2, s. 024306-
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Tidskriftsartikel (refereegranskat)abstract
- A photochemistry study on nitrous oxide making use of site-selective excitation of terminal nitrogen, central nitrogen, and oxygen 1s -> 3 pi excitations is presented. The resonant Auger decay which takes place following excitation can lead to dissociation of the N2O+ ion. To elucidate the nuclear dynamics, energy-resolved Auger electrons were detected in coincidence with the ionic dissociation products, and a strong dependence of the fragmentation pathways on the core-hole site was observed in the binding energy region of the first satellite states. A description based on the molecular orbitals as well as the correlation between the thermodynamical thresholds of ion formation and the first electronic states of N2O+ has been used to qualitatively explain the observed fragmentation patterns.
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| 2. |
- Bao, Zhuo, et al.
(författare)
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Detailed Theoretical and Experimental Description of Normal Auger Decay in O2
- 2008
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 41:12, s. 125101-
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Tidskriftsartikel (refereegranskat)abstract
- The normal Auger electron spectrum of the O-2 molecule is assigned in detail on the basis of ab initio valence configuration interaction (CI) wavefunctions. Potential energy curves of the ground state, the core-ionized states and the doubly charged final states are calculated and Auger decay rates are obtained with the one-centre approximation. Using the lifetime vibrational interference method, band shapes are obtained for all contributions to the Auger spectrum. The calculated Auger electron spectrum allows us to identify all features observed experimentally. Significant differences to previous assignments are reported. A quantitative simulation of the spectrum is given on the basis of a curve-fitting procedure, in which the energetic positions and intensities of the theoretical bands were optimized. Besides providing a basis for a refined analysis of the spectrum, the fit allows us to assess the accuracy of the calculation. As expected for this level of theory, the absolute accuracy of the valence CI energies is found to be about 0.3 eV. The inherent error of the one-centre transition rates is less than 5% of the most intense transition in the spectrum. The frequently questioned one-centre Auger transition rates are shown to be rather appropriate if applied with reasonable wavefunctions and if the vibrational band structure of the molecular spectrum is properly taken into account.
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| 3. |
- Bao, Zhuo, 1977-
(författare)
-
Synchrotron Radiation Studies of Free and Adsorbed Molecules
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis contains two parts. The first part concerns the research work on free molecules using synchrotron-radiation-related techniques. Auger electron spectra of two free open-shell molecules, O2 and NO, were studied experimentally and theoretically. Photoionization experimental technique with tunable synchrotron radiation source was used to induce core-level electron ionization and obtain the KVV normal Auger electron spectra. A quantitative assignment of O2 normal Auger spectrum was obtained by applying ab initio CI calculations and LVI Auger line shape simulations including the bond length dependence of Auger transition rates. The photon energy dependence of normal Auger electron spectra was focused on with photon energies in the vicinities of core-ionization threshold energies. Consequently, the MAPCI (Molecular Auger Post Collision Interaction) theory was developed. Taking the near-threshold O2 normal Auger spectrum as an example, the two extreme cases of MAPCI effect, “atomic-like PCI” and “molecular PCI”, were discovered and discussed. The effect of shape resonance on near-threshold molecular normal Auger spectrum was discussed taking NO near threshold normal Auger spectra as example.The second part deals with research work on the chemisorption of small epoxy organic molecules, ethylene oxide, methyl oxirane, on Si (100) surfaces. Synchrotron radiation related techniques, UPS, XPS and NEXAFS, were applied. Based on the valence photoemission spectra, C 1s and Si 2p XPS spectra, the epoxy ring opening reactions of these molecules in chemisorption process were proved. Further tentative search for the surface-adsorbate CDAD effect was performed, and no evident circular dichroism was confirmed.
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| 4. |
- Bergersen, Henrik, et al.
(författare)
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First observation of vibrations in core-level photoelectron spectra of free neutral molecular clusters
- 2006
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 429:1-3, s. 109-113
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Tidskriftsartikel (refereegranskat)abstract
- Core-level photoelectron spectra of free neutral methane clusters have been recorded. These spectra exhibit well-resolved surface and bulk features as well as vibrational fine structure. The vibrational structure in the cluster signal is well reproduced by a theoretical model that assumes independent contributions from inter- and intramolecular modes. The intramolecular contribution to the vibrational line-shape is taken to be equal to that of the monomer in the gas phase, while the intermolecular part is simplified to line broadening. An estimate of the cluster size has been made on the basis of the observed surface-to-bulk intensity ratio.
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| 5. |
- Céolin, Denis, et al.
(författare)
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A rotatable electron spectrometer for multicoincidence experiments
- 2010
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 81:6
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Tidskriftsartikel (refereegranskat)abstract
- We have developed a rotatable hemispherical spectrometer with good energy and angular resolution, which can be positioned with the lens axis arbitrarily within a solid angle of 1 pi. The collection angle of the emitted electrons with respect to the polarization axis of the light is set by means of a three-axes goniometer, operating under vacuum. An important requirement for this setup was the possibility to perform coincidences between the electron analyzed by the spectrometer and one or several other particles, such as ions, electrons, or photons. The lens system and the hemispheres have been designed to accommodate such experimental demands, regarding parameters such as the resolving power, the acceptance angle, or the width of the kinetic energy window which can be recorded for a given pass energy. We have chosen to detect the impact position of the electron at the focal plane of the hemispherical analyzer with a delay line detector and a time-to-digital converter as acquisition card rather than using a conventional charge-coupled device camera. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3449333]
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| 6. |
- Céolin, Denis, et al.
(författare)
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Auger electron-ion coincidence studies to probe molecular dynamics
- 2004
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048. ; 141:2-3, s. 171-181
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Tidskriftsartikel (refereegranskat)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 N-2 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.
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| 7. |
- Ceolin, Denis, et al.
(författare)
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Effect of the Cl2p core orbital excitation on the nuclear dynamics of the three dichloroethylene isomers
- 2011
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 184:1-2, s. 24-28
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Tidskriftsartikel (refereegranskat)abstract
- In this article, we present the X-ray absorption spectra of the three isomers of dichloroethylene C2H2Cl2 in the vicinity of the chlorine L-2 and L-3 edges. These isomers were excited along the first Cl2p to lowest unoccupied molecular orbital transition and an analysis of the corresponding resonant Auger spectra shows that the C-Cl bond can break before the electronic decay. An investigation of a possible Auger Doppler-like effect is also presented.
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| 8. |
- Ceolin, Denis, et al.
(författare)
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Fragmentation of methyl chloride studied by partial positive and negative ion-yield spectroscopy
- 2007
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 126:8, s. 084309-
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Tidskriftsartikel (refereegranskat)abstract
- The authors present partial-ion-yield experiments on the methyl chloride molecule excited in the vicinity of the C12p and C1s inner shells. A large number of fragments, cations produced by dissociation or recombination processes, as well as anionic species, have been detected. Although the spectra exhibit different intensity distributions depending on the core-excited atom, general observations include strong site-selective fragmentation along the C-Cl bond axis and a strong intensity dependence of transitions involving Rydberg series on fragment size.
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| 9. |
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| 10. |
- Céolin, Denis, et al.
(författare)
-
Recoil-induced ultrafast molecular rotation probed by dynamical rotational Doppler effect
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Observing and controlling molecular motion, and in particular rotation,is a fundamental topic in physics and chemistry. In order toinitiate ultrafast rotation, one needs a way to transfer a large angularmomentum to the molecule. As a showcase, this was performedby hard x-ray C1s ionization of carbon monoxide, accompanied byspinning-up the molecule via the recoil “kick” of the emitted fast photoelectron.To visualize this molecular motion, we use the dynamicalrotational Doppler effect and an X-ray “pump-probe” device offeredby nature itself: the recoil-induced ultrafast rotation is probed by subsequentAuger electron emission. The time information in our experimentorigins from the natural delay between the C1s photoionizationinitiating the rotation and the ejection of the Auger electron. From amore general point of view, time-resolved measurements can be performedin two ways: either to vary the "delay" time as in conventionaltime-resolved pump-probe spectroscopy and to use the dynamicsgiven by the system, or to keep constant "delay" time and to manipulatethe dynamics. Since in our experiment we cannot change the delaytime given by the core-hole lifetime $\tau$, we use the second optionand control the rotational speed by changing the kinetic energy of thephotoelectron. The recoil-induced rotational dynamics controlled insuch a way is observed as a photon-energy dependent asymmetryof the Auger lineshape, in full agreement with theory. This asymmetryis explained by a significant change of the molecular orientationduring the core-hole lifetime, which is comparable with the rotationalperiod.
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| 11. |
- Ceolin, Denis, et al.
(författare)
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Recoil-induced ultrafast molecular rotation probed by dynamical rotational Doppler effect
- 2019
-
Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : NATL ACAD SCIENCES. - 0027-8424 .- 1091-6490. ; 116:11, s. 4877-4882
-
Tidskriftsartikel (refereegranskat)abstract
- Observing and controlling molecular motion and in particular rotation are fundamental topics in physics and chemistry. To initiate ultrafast rotation, one needs a way to transfer a large angular momentum to the molecule. As a showcase, this was performed by hard X-ray C1s ionization of carbon monoxide accompanied by spinning up the molecule via the recoil "kick" of the emitted fast photoelectron. To visualize this molecular motion, we use the dynamical rotational Doppler effect and an X-ray "pump-probe" device offered by nature itself: the recoil-induced ultrafast rotation is probed by subsequent Auger electron emission. The time information in our experiment originates from the natural delay between the C1s photoionization initiating the rotation and the ejection of the Auger electron. From a more general point of view, time-resolved measurements can be performed in two ways: either to vary the "delay" time as in conventional time-resolved pump-probe spectroscopy and use the dynamics given by the system, or to keep constant delay time and manipulate the dynamics. Since in our experiment we cannot change the delay time given by the core-hole lifetime tau, we use the second option and control the rotational speed by changing the kinetic energy of the photoelectron. The recoil-induced rotational dynamics controlled in such a way is observed as a photon energy-dependent asymmetry of the Auger line shape, in full agreement with theory. This asymmetry is explained by a significant change of the molecular orientation during the core-hole lifetime, which is comparable with the rotational period.
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| 12. |
- Ceolin, Denis, et al.
(författare)
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Site-selective resonant Auger spectroscopy of iso-dichloroethylene at the carbon K-edge
- 2012
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 185:8-9, s. 252-258
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Tidskriftsartikel (refereegranskat)abstract
- This study focuses on the two C1s-to-LUMO (lowest unoccupied molecular orbital) excitations of the iso-dichloroethylene (H2C=CCl2) and the subsequent Auger decay. We investigate the effect of the two different carbon core excitations on the population of the cation produced after electronic relaxation. The resonant Auger spectra are interpreted by comparison to the valence shells photoionization spectrum and with the help of theoretical calculations. Several consequences of the core-hole localization on the electronic decay are observed. In particular, the resonant excitation of the C1s(CH2) to the LUMO leads to a large intensity increase in the region of the first satellite state, whereas no dramatic changes are observed for the C1s(CCl2) excitation.
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| 13. |
- Goldsztejn, Gildas, et al.
(författare)
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Electronic state-lifetime interference in resonant Auger spectra : a tool to disentangle overlapping core-excited states
- 2016
-
Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 18:22, s. 15133-15142
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Tidskriftsartikel (refereegranskat)abstract
- We have measured resonant-Auger decay following Cl 1s(-1) excitations in HCl and CH3Cl molecules, and extracted the pseudo-cross sections of different Cl 2p(-2) final states. These cross sections show clear evidence of shake processes as well as contributions of electronic state-lifetime interference (ELI). To describe the spectra we developed a fit approach that takes into account ELI contributions and ultrafast nuclear dynamics in dissociative core-excited states. Using this approach we utilized the ELI contributions to obtain the intensity ratios of the overlapping states Cl 1s(-1)4p pi/1s(-1)4p sigma in HCl and Cl 1s(-1)4pe/1s(-1)4pa(1) in CH3Cl. The experimental value for HCl is compared with theoretical results showing satisfactory agreement.
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| 14. |
- Gopakumar, Geethanjali, et al.
(författare)
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Probing aqueous ions with non-local Auger relaxation
- 2022
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 24:15, s. 8661-8671
-
Tidskriftsartikel (refereegranskat)abstract
- Non-local analogues of Auger decay are increasingly recognized as important relaxation processes in the condensed phase. Here, we explore non-local autoionization, specifically Intermolecular Coulombic Decay (ICD), of a series of aqueous-phase isoelectronic cations following 1s core-level ionization. In particular, we focus on Na+, Mg2+, and Al3+ ions. We unambiguously identify the ICD contribution to the K-edge Auger spectrum. The different strength of the ion-water interactions is manifested by varying intensities of the respective signals: the ICD signal intensity is greatest for the Al3+ case, weaker for Mg2+, and absent for weakly-solvent-bound Na+. With the assistance of ab initio calculations and molecular dynamics simulations, we provide a microscopic understanding of the non-local decay processes. We assign the ICD signals to decay processes ending in two-hole states, delocalized between the central ion and neighbouring water. Importantly, these processes are shown to be highly selective with respect to the promoted water solvent ionization channels. Furthermore, using a core-hole-clock analysis, the associated ICD timescales are estimated to be around 76 fs for Mg2+ and 34 fs for Al3+. Building on these results, we argue that Auger and ICD spectroscopy represents a unique tool for the exploration of intra- and inter-molecular structure in the liquid phase, simultaneously providing both structural and electronic information.
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| 15. |
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| 16. |
- Johansson, Fredrik, et al.
(författare)
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Resonant Auger spectroscopy on solid xenon on gold, silver, and copper substrates
- 2023
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Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : American Physical Society (APS). - 2469-9926 .- 2469-9934. ; 107:3
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Tidskriftsartikel (refereegranskat)abstract
- An investigation of the radiationless decay of core excited Xe atoms in the region of Xe L3M4,5M4,5 Auger electron kinetic energies (using x-ray energies in the vicinity of the L3 threshold) is presented for Xe adsorbed on Cu, Ag, and Au. The intensity distribution of the decay channels is different compared with Xe in the gas phase. Charge transfer of the core excited electron occurs within tens of attoseconds in all systems for excitation energies approaching the ionization threshold of the condensed system, whereas charge transfer times are substrate-dependent for lower excitation energies. The determination of partial yields into the decay channels allows for the observation of a decay channel present in the Xe/Cu and Xe/Ag systems but not in the case of Xe/Au. Theoretical calculations allow us to interpret this difference as emanating from varying amounts of the ground state hybridization between Xe and the substrates, which impacts the energy of the Auger final states enabling identification of these states giving rise to system specific features in the experimental data.
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| 17. |
- Journel, Loïc, et al.
(författare)
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Resonant double Auger decay in carbon K-shell excitation of CO
- 2008
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Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 77:4, s. 14-042710
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Tidskriftsartikel (refereegranskat)abstract
- We have studied double Auger decay after C 1s→2 photoexcitation in gas phase carbon monoxide. Two distinct processes, namely direct double Auger decay and cascade double Auger decay, are identified and studied in detail using multiple coincidence techniques. Cascade Auger decay is shown to be the overall dominant process. Decay channels involving the dissociation of the molecule followed by autoionization of the oxygen fragments are observed.
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| 18. |
- Kawerk, Elie, et al.
(författare)
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Resonant inelastic x-ray scattering on iso-C2H2Cl2 around the chlorine K-edge : Structural and dynamical aspects
- 2014
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 141:14, s. 144301-
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Tidskriftsartikel (refereegranskat)abstract
- We report a theoretical and experimental study of the high resolution resonant K-alpha X-ray emission lines around the chlorine K-edge in gas phase 1,1-dichloroethylene. With the help of ab initio electronic structure calculations and cross section evaluation, we interpret the lowest lying peak in the X-ray absorption and emission spectra. The behavior of the K-alpha emission lines with respect to frequency detuning highlights the existence of femtosecond nuclear dynamics on the dissociative Potential Energy Surface of the first K-shell core-excited state.
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| 19. |
- Laksman, Joakim, et al.
(författare)
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Development and characterization of a multiple-coincidence ion-momentum imaging spectrometer.
- 2013
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 84:12
-
Tidskriftsartikel (refereegranskat)abstract
- The design and performance of a high-resolution momentum-imaging spectrometer for ions which is optimized for experiments using synchrotron radiation is presented. High collection efficiency is achieved by a focusing electrostatic lens; a long drift tube improves mass resolution and a position-sensitive detector enables measurement of the transverse momentum of ions. The optimisation of the lens for particle momentum measurement at the highest resolution is described. We discuss the overall performance of the spectrometer and present examples demonstrating the momentum resolution for both kinetics and for angular measurements in molecular fragmentation for carbon monoxide and fullerenes. Examples are presented that confirm that complete space-time focussing is possible for a two-field three-dimensional imaging spectrometer.
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| 20. |
- Laksman, Joakim, et al.
(författare)
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Dynamics of proton migration and dissociation in core-excited ethyne probed by multiple ion momentum imaging
- 2009
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 131:24, s. 1-244305
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Tidskriftsartikel (refereegranskat)abstract
- The study focuses on the rapid geometry change in ethyne, excited near the carbon 1s edge. Core excitation and ionization leads to population of dicationic states in ethyne. We study three competing dissociation pathways associated with deprotonation in the linear ethyne molecule, and two cases of rapid proton migration. We investigate the alignment of the molecule in the excited state, and find startling differences in these three cases. We present evidence for a strong anisotropy in the production of H+2 /C+2 fragments through a rapid deformation of the molecule to a dibridged conformation with the transition dipole moment parallel to the polarization of the exciting radiation.
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| 21. |
- Laksman, Joakim, et al.
(författare)
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Nuclear motion in carbonyl sulfide induced by resonant core electron excitation
- 2010
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 133:14, s. 1-144314
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Tidskriftsartikel (refereegranskat)abstract
- The angular anisotropy for selected dissociation channels is measured at resonantly excited states of and symmetries at the C and O K-shell ionization edges of carbonyl sulfide. While the kinetic energy released in the reaction is mainly independent of the excitation energy, the angular anisotropy and momentum correlation clearly show deformation of the OCS molecule in the C1s−Pi state. The discovery of a two-body fragmentation channel SO+/C+ with a well defined angular anisotropy indicates the rapid formation of the CSO isomeric species.
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| 22. |
- Laksman, Joakim, et al.
(författare)
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Rapid bond rearrangement in core-excited molecular water.
- 2013
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 15:44, s. 19322-19329
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Tidskriftsartikel (refereegranskat)abstract
- The angular anisotropy of fragments created in the dissociation of core-electron excited water molecules is studied to probe the correlation between fragmentation channels, kinematics and molecular geometry. We present fragment kinetic measurements for water molecules where the inner-shell oxygen electron is excited to the unoccupied 4a1 and 2b2 valence molecular orbitals. The kinematics of individual fragmentation channels are measured using fully three-dimensional momentum imaging of fragments. The results show that the geometry of the molecule and the kinetic energy of fragments are strongly coupled in the atomisation process. In addition we identify a fragmentation process arising from bond rearrangement evidenced by the H2(+)-O(+) ion pair which is accessible for resonant excitation of the 1s electron. In all of the two-body fragmentation processes the dissociation takes place along the potential-energy surface, while atomisation reveals both dissociation along the potential surface and Coulomb explosion. The angular distribution of fragments suggests that the bond rearrangement is very rapid; likely on a sub 10 fs time scale.
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| 23. |
- Le Guen, K, et al.
(författare)
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Development of a four-element conical electron lens dedicated to high resolution Auger electron-ion(s) coincidence experiments
- 2002
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 1089-7623 .- 0034-6748. ; 73:11, s. 3885-3894
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Tidskriftsartikel (refereegranskat)abstract
- A four-element conical electron lens has been developed in view of its integration to a double toroidal electron energy analyzer (DTA) dedicated to Auger electron-ion coincidence measurements. The lens design, using electron trajectory numerical simulations, was entirely guided by the perspective of analyzing energetic electrons with high resolution in the multicoincidence regime. The design, construction, and experimental characterization stages of this electron optics system are described in this article. Emphasis is put on the importance of third generation synchrotron radiation sources when performing such multicoincidence experiments.
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| 24. |
- Le Guen, K., et al.
(författare)
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H2S ultrafast dissociation probed by energy-selected resonant Auger electron–ion coincidence measurements
- 2007
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 127:11, s. 114315-
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Tidskriftsartikel (refereegranskat)abstract
- We have studied the ultrafast dissociation of the H2S molecule upon S 2p(3/2)-> 6a(1) inner-shell excitation by combining high-resolution resonant Auger spectroscopy and energy-selected Auger electron-ion coincidence measurements. Auger final states have been correlated to the different fragmentation pathways (S+, HS+, and H2S+ ions). As an original result, we evidence a three-step mechanism to describe the resonant production of S+: the Auger recombination in the HS* fragment is followed for the A (3)Pi and c (1)Pi states by the S++H fragmentation mechanism.
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| 25. |
- Le Guen, K, et al.
(författare)
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Influence of formation path on the CH2BrCl2+ dissociation dynamics
- 2005
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 123:8
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Tidskriftsartikel (refereegranskat)abstract
- To get further insight into the CH2BrCl site-selective fragmentation previously observed upon inner-shell ionization, we have performed high-resolution Br 3d and Cl 2p Auger and spin-orbit resolved Br 3d Auger spectra, and studied the dissociation properties of the CH2BrCl2+ dication formed at threshold by means of threshold electron pair-ion coincidence measurements. The key point is that the origin of site-specific bond breaking is found in the Auger decay itself, as it preferentially populates selected dication states. Whereas the predominance of the C-Br bond breaking is observed in both threshold and inner-shell studies, no signature of selective C-Cl rupture is reported for the dication formed at threshold.
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| 26. |
- Miron, Catalin, et al.
(författare)
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Multipathway dissociation dynamics of core-excited methyl chloride probed by high resolution electron spectroscopy and Auger-electron-ion coincidences
- 2008
-
Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 128:15, s. 154314-
-
Tidskriftsartikel (refereegranskat)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.
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| 27. |
- Miteva, Tsveta, et al.
(författare)
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The All-Seeing Eye of Resonant Auger Electron Spectroscopy : A Study on Aqueous Solution Using Tender X-rays
- 2018
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Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 9:15, s. 4457-4462
-
Tidskriftsartikel (refereegranskat)abstract
- X-ray absorption and Auger electron spectroscopies are demonstrated to be powerful tools to unravel the electronic structure of solvated ions. In this work for the first time, we use a combination of these methods in the tender X-ray regime. This allowed us to address electronic transitions from deep core levels, to probe environmental effects, specifically in the bulk of the solution since the created energetic Auger electrons possess large mean free paths, and moreover, to obtain dynamical information about the ultrafast delocalization of the core-excited electron. In the considered exemplary aqueous KCl solution, the solvated isoelectronic K+ and Cl- ions exhibit notably different Auger electron spectra as a function of the photon energy. Differences appear due to dipole-forbidden transitions in aqueous K+ whose occurrence, according to the performed ab initio calculations, becomes possible only in the presence of solvent water molecules.
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| 28. |
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| 29. |
- Mocellin, Alexandra, et al.
(författare)
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Site selective dissociation upon core ionization of ozone
- 2007
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 435:4-6, s. 214-218
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Tidskriftsartikel (refereegranskat)abstract
- Ozone is found to exhibit substantial site-selective fragmentation when its fragment ions are collected in coincidence with energy selected electrons. We find a preferential production of the O-2(+)/O+(O+/O+) ion pair upon ionization of the terminal (central) oxygen Is electron. Depending on the hole localization, Auger rates are different towards the various final states of the dication, which would produce the observed different fragmentation pattern. We also observe however an increase O-2(+)/O+ production for when the terminal core-hole state is vibrationally excited. This shows the role of the nuclear motion before the Auger decay in the observed site-specific.
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| 30. |
- Mosaferi, Mohammadreza, et al.
(författare)
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Fingerprint of Dipole Moment Orientation of Water Molecules in Cu2+ Aqueous Solution Probed by X-ray Photoelectron Spectroscopy
- 2024
-
Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126.
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure and geometrical organization of aqueous Cu2+ have been investigated by using X-ray photoelectron spectroscopy (XPS) at the Cu L-edge combined with state-of-the-art ab initio molecular dynamics and a quantum molecular approach designed to simulate the Cu 2p X-ray photoelectron spectrum. The calculations offer a comprehensive insight into the origin of the main peak and satellite features. It is illustrated how the energy drop of the Cu 3d levels (≈7 eV) following the creation of the Cu 2p core hole switches the nature of the highest singly occupied molecular orbitals (MOs) from the dominant metal to the dominant MO nature of water. It is particularly revealed how the repositioning of the Cu 3d levels induces the formation of new bonding (B) and antibonding (AB) orbitals, from which shakeup mechanisms toward the relaxed H-SOMO operate. As highlighted in this study, the appearance of the shoulder near the main peak corresponds to the characteristic signature of shakeup intraligand (1a1 → H-SOMO(1b1)) excitations in water, providing insights into the average dipole moment distribution (≈36°) of the first-shell water molecules surrounding the metal ion and its direct impact on the broadening of the satellite. It is also revealed that the main satellite at 8 eV from the main peak corresponds to (metal/1b2 → H-SOMO(1b1) of water) excitations due to a bonding/antibonding (B/AB) interaction of Cu 3d levels with the deepest valence O2p/H1s 1b2 orbitals of water. This finding underscores the sensitivity of XPS to the electronic structure and orientation of the nearest water molecules around the central ion.
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| 31. |
- Piancastelli, Maria Novella, et al.
(författare)
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A High-resolution Study of Resonant Auger Decay Processes in N2O After Core Electron Excitation from Terminal Nitrogen, Central Nitrogen and Oxygen Atoms to the 3π LUMO
- 2007
-
Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 40:17, s. 3357-3365
-
Tidskriftsartikel (refereegranskat)abstract
- Decay spectra of N2O following excitation to the N terminal (Nt) → π*, N central (Nc) → π* and O is → π* intermediate states are reported. The final states reached after participator decay show resonant enhancement consistent with a local-density-of-states analysis based on the Mulliken population of the valence molecular orbitals. In particular, the X-state is resonantly enhanced mostly after excitation from the Nt 1s and the O Is core levels to the π*, while the B-state is mostly enhanced following the excitation of the Nc Is → π* intermediate state. Below the Nt Is threshold, the lowest lying peak related to spectator decay falls at lower binding energy than the highest lying participator peak. This can be attributed to a particularly strong screening effect exerted by the excited electron in the LUMO.
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| 32. |
- Piancastelli, Maria Novella, et al.
(författare)
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Core-hole-clock spectroscopies in the tender x-ray domain
- 2014
-
Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 47:12, s. 124031-
-
Tidskriftsartikel (refereegranskat)abstract
- The core-hole-clock method to observe dynamical phenomena in molecular photoexcitation on the 1 fs-hundreds-of-attoseconds time scale is illustrated with examples from resonant inelastic x-ray scattering (RIXS) and resonant-Auger-emission experiments on the prototypical CH3Cl system in the tender x-ray domain. In particular, a direct comparison between RIXS and resonant-Auger data allows us to unravel subtle details of nuclear motion and interplay of potential curves of the intermediate and final states reached upon deep-core excitation.
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| 33. |
- Piancastelli, Maria Novella, et al.
(författare)
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Electronic and Geometric Structure of Methyl Oxirane Adsorbed on Si (100) 2 × 1
- 2007
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 254:1, s. 108-112
-
Tidskriftsartikel (refereegranskat)abstract
- Electronic and geometric properties of the adsorbate–substrate complex formed upon adsorption of methyl oxirane on Si(1 0 0)2 × 1 at room temperature is reported, obtained with synchrotron radiation-induced valence and core-level photoemission. A ring-opening reaction is demonstrated to occur, followed by a five-membered ring formation involving two of the Si surface atoms bound to a surface dimer. Core-level photoemission spectra support the ring-opening reaction and the SiO and SiC bond formation, while from the valence spectra a more extended molecular fragmentation can be ruled out. We discuss the most likely geometry of the five-membered ring.
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| 34. |
- Piancastelli, Maria Novella, et al.
(författare)
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Electronic Structure of Core-excited and Core-ionized Methyl Oxirane
- 2007
-
Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 156, s. 259-264
-
Tidskriftsartikel (refereegranskat)abstract
- We report a detailed analysis of the electronic structure of methyl oxirane, including core-level photoelectron spectroscopy, X-ray absorption at both C and O K-shells, resonant Auger and normal Auger spectroscopy. The X-ray absorption spectra (XAS) around the C K-edge can be easily interpreted on the ground of the chemical shift between the carbon atoms with different chemical environments. The X-ray absorption data around the O K-edge are quite structureless, hinting for a likely fragmentation process (possibly implying a ring-opening reaction). In resonant Auger spectra obtained after excitation below both the C 1s and O 1s ionization thresholds we notice a predominance of spectator decay implying a strong mixing between empty molecular orbitals and Rydberg states.
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| 35. |
- Piancastelli, Maria Novella, et al.
(författare)
-
Partial cation and anion-yield experiments in ammonia around the N 1s ionization threshold
- 2007
-
Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 155:1-3, s. 86-90
-
Tidskriftsartikel (refereegranskat)abstract
- We report partial cation and anion-yield measurements around the N K edge in isolated ammonia molecules. Due to the dominance of spectator electronic decay following Rydberg excitations, fragmentation was found to be more extensive following excitation to intermediate states of Rydberg character compared to excitation of states with molecular-orbital character. Unusual stability of the NH32+ fragment produced directly above threshold by normal-Auger decay is attributed to a stable planar geometry induced by a specific electronic configuration. Hydrogen anions are not detected above threshold except following the decay of resonant doubly excited neutral states embedded in the K-shell ionization continuum.
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| 36. |
- Puettner, Ralph, et al.
(författare)
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Direct Observation of Double-Core-Hole Shake-Up States in Photoemission
- 2015
-
Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 114:9
-
Tidskriftsartikel (refereegranskat)abstract
- Direct measurements of Ar+ 1s(-1)2p(-1)nl double-core-hole shake-up states are reported using conventional single-channel photoemission, offering a new and relatively easy means to study such species. The high-quality results yield accurate energies and lifetimes of the double-core-hole states. Their photoemission spectrum also can be likened to 1s absorption of an exotic argon ion with a 2p core vacancy, providing new information about the spectroscopy of both this unusual ionic state as well as the neutral atom.
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| 37. |
- Puettner, Ralph, et al.
(författare)
-
Si 1s(-1), 2s(-1) and 2p(-1) lifetime broadening of SiX4 (X = F, Cl, Br, CH3) molecules : SiF4 anomalous behaviour reassessed
- 2019
-
Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : ROYAL SOC CHEMISTRY. - 1463-9076 .- 1463-9084. ; 21:17, s. 8827-8836
-
Tidskriftsartikel (refereegranskat)abstract
- The Si 1s(-1), Si 2s(-1), and Si 2p(-1) photoelectron spectra of the SiX4 molecules with X = F, Cl, Br, CH3 were measured. From these spectra the Si 1s(-1) and Si 2s(-1) lifetime broadenings were determined, revealing a significantly larger value for the Si 2s(-1) core hole of SiF4 than for the same core hole of the other molecules of the sequence. This finding is in line with the results of the Si 2p(-1) core holes of a number of SiX4 molecules, with an exceptionally large broadening for SiF4. For the Si 2s(-1) core hole of SiF4 the difference to the other SiX4 molecules can be explained in terms of Interatomic Coulomb Decay (ICD)-like processes. For the Si 2p(-1) core hole of SiF4 the estimated values for the sum of the Intraatomic Auger Electron Decay (IAED) and ICD-like processes are too small to explain the observed linewidth. However, the results of the given discussion render for SiF4 significant contributions from Electron Transfer Mediated Decay (ETMD)-like processes at least plausible. On the grounds of our results, some more molecular systems in which similar processes can be observed are identified.
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| 38. |
- Ristinmaa Sörensen, Stacey, et al.
(författare)
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Rapid bond rearrangement in molecules after core-electron excitation
- 2014
-
Ingår i: XXVIII International Conference on Photonic, Electronic and Atomic Collisions (ICPEAC 2013). - : IOP Publishing. - 1742-6596 .- 1742-6588. ; 488, s. 012006-012006
-
Konferensbidrag (refereegranskat)abstract
- Experimental studies of core-excited molecules using three-dimensional multi particle momentum imaging are presented where bond rearrangement processes in dication species are analysed. The aim of the study is to understand the relation between the geometric changes associated with core-excited states and the kinetic energy released in particular molecular dissociation processes. The kinematics of individual fragmentation channels are studied by fully three-dimensional momentum imaging of fragments in coincidence. Examples are presented where the high efficiency of the instrument and the fully three-dimensional momentum capabilities are exploited to understand nuclear motion leading to bond rearrangement in core-excited states. We identify bond-rearrangement processes in water, carbonyl sulphide and acetylene which are initiated in the core-excited state. In water this is evidenced by the H-2(+)/O+ ion pair, and in carbonyl sulphide the OS++C+ pair is the fingerprint of this reaction. In acetylene the H-2(+) + C-2(+) ion pair indicates a molecular geometry that changes from linear to strongly bent. We measure the angular distribution of all fragments and fragment pairs and for the bond rearrangement processes in water and in core-excited acetylene the angular distribution of fragments suggests that the bond rearrangement is very rapid.
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| 39. |
- Simon, Marc, et al.
(författare)
-
Atomic Auger Doppler effects upon emission of fast photoelectrons
- 2014
-
Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 5, s. 4069-
-
Tidskriftsartikel (refereegranskat)abstract
- Studies of photoemission processes induced by hard X-rays including production of energetic electrons have become feasible due to recent substantial improvement of instrumentation. Novel dynamical phenomena have become possible to investigate in this new regime. Here we show a significant change in Auger emission following 1s photoionization of neon, which we attribute to the recoil of the Ne ion induced by the emission of a fast photoelectron. Because of the preferential motion of the ionized Ne atoms along two opposite directions, an Auger Doppler shift is revealed, which manifests itself as a gradual broadening and doubling of the Auger spectral features. This Auger Doppler effect should be a general phenomenon in high-energy photoemission of both isolated atoms and molecules, which will have to be taken into account in studies of other recoil effects such as vibrational or rotational recoil in molecules, and may also have consequences in measurements in solids.
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| 40. |
- Svanström, Sebastian, et al.
(författare)
-
Direct Measurements of Interfacial Photovoltage and Band Alignment in Perovskite Solar Cells Using Hard X-ray Photoelectron Spectroscopy
- 2023
-
Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 15:9, s. 12485-12494
-
Tidskriftsartikel (refereegranskat)abstract
- A heterojunction is the key junction for charge extraction in many thin film solar cell technologies. However, the structure and band alignment of the heterojunction in the operating device are often difficult to predict from calculations and, due to the complexity and narrow thickness of the interface, are difficult to measure directly. In this study, we demonstrate a technique for direct measurement of the band alignment and interfacial electric field variations of a fully functional lead halide perovskite solar cell structure under operating conditions using hard X-ray photoelectron spectroscopy (HAXPES). We describe the design considerations required in both the solar cell devices and the measurement setup and show results for the perovskite, hole transport, and gold layers at the back contact of the solar cell. For the investigated design, the HAXPES measurements suggest that 70% of the photovoltage was generated at this back contact, distributed rather equally between the hole transport material/gold interface and the perovskite/hole transport material interface. In addition, we were also able to reconstruct the band alignment at the back contact at equilibrium in the dark and at open circuit under illumination.
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| 41. |
- Travnikova, Oksana, et al.
(författare)
-
A Study of Substituent Effects for Aliphatic CH3-X Compounds by Resonant Auger Spectroscopy
- 2009
-
Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 11:5, s. 826-833
-
Tidskriftsartikel (refereegranskat)abstract
- In this study linear free energy relationships (LFER) are applied to the relaxation of core-excited states in aliphatic CH3X compounds. There are at least two valence orbitals involved in Auger decay following CCH31s →σ*C–X excitation, which may as well be localized on the substituents in this series. Therefore, the observed property cannot be strictly attached to the so-called reaction center. The behavior of substituent constants in the description of core-hole processes in aliphatic compounds is also checked on C1s ionization potentials for the extended series of substituted methanes. The role of the inductive effect for both resonant Auger kinetic energies (Ek) and C1s binding energies (Ecoreb) is very important. CCH31s →σ*C–X excitation energies do not show any significant correlations with inductive substituent constants. On the contrary, Taft’s inductive parameters alone give good correlations for Ek. A simple model with ‘Z + 1’ approximation is developed to describe Ek and explain the observed correlations:Ek = Ecoreb− (Ev(Z)b + Eea(Z+1)+),where Ebv(Z) is the valence ionization potential for CH3X and Eea(Z+1)+ is the electron affinity for [NH3X]+.
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| 42. |
- Travnikova, Oksana, et al.
(författare)
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Assignment of the L2,3VV normal Auger decay spectrum of Cl-2 by ab initio calculations
- 2009
-
Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 474:1-3, s. 67-73
-
Tidskriftsartikel (refereegranskat)abstract
- Auger decay processes of the Cl 2p ionized states have been studied in Cl-2 by means of high- resolution electron spectroscopy and ab initio calculations. This led to reassignment of the normal L2,3VV Auger decay spectrum of Cl2. The reliability of this assignment is strongly supported by an independent measurement of the L2; 3VV Auger electron spectrum of Cl2 which has been obtained after selective Cl 2p(3/2)(-1) photoionization of the chlorine molecule. Partial Auger transition rates for the three nongenerate spin-orbit and molecular- field- split 2p(-1) states - 2p(3/2,3/2)(-1) ((2)Pi(3/2)), 2p(3/2,1/2)(-1)((2)Sigma(+)(1/2)) and 2p(1/2,1/2)(-1)((2)Pi(1/2)) - show differences similar to the ones reported in previous works for HCl.
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| 43. |
- Travnikova, Oksana, et al.
(författare)
-
Disentangling the complex line profiles in the Cl 2p photoelectron spectra of Cl-2
- 2006
-
Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 426:4-6, s. 452-458
-
Tidskriftsartikel (refereegranskat)abstract
- High-resolution Cl (2p) photoelectron spectra Of Cl-2 are reported and their complex structure is analyzed in detail, taking into account molecular field (NIF), spin-orbit (SO) and parity splitting. High-level ab initio calculations were performed to provide reliable values for spectroscopic parameters. Accurate data analysis enabled us to determine the value of molecular-field splitting of 86 7 meV, and values of 92 5, 79 11 and 105 12 meV for the lifetime line widths of the (2)Pi(1/2), (2)Sigma(+)(1/2) and (2)Pi(3/2) states, respectively. The gerade-ungerade splitting of less than 5 meV is obtained from the calculations.
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| 44. |
- Travnikova, Oksana, et al.
(författare)
-
Energy-Dependent Relative Cross Sections in Carbon 1s Photoionization : Separation of Direct Shake and Inelastic Scattering Effects in Single Molecules
- 2019
-
Ingår i: Journal of Physical Chemistry A. - : AMER CHEMICAL SOC. - 1089-5639 .- 1520-5215. ; 123:35, s. 7619-7635
-
Tidskriftsartikel (refereegranskat)abstract
- We demonstrate that the possibility of monitoring relative photoionization cross sections over a large photon energy range allows us to study and disentangle shake processes and intramolecular inelastic scattering effects. In this gas-phase study, relative intensities of the carbon 1s photoelectron lines from chemically inequivalent carbon atoms in the same molecule have been measured as a function of the incident photon energy in the range of 300-6000 eV. We present relative cross sections for the chemically shifted carbon 1s lines in the photoelectron spectra of ethyl trifluoroacetate (the "ESCA" molecule). The results are compared with those of methyl trifluoroacetate and S-ethyl trifluorothioacetate as well as a series of chloro-substituted ethanes and 2-butyne. In the soft X-ray energy range, the cross sections show an extended X-ray absorption fine structure type of wiggles, as was previously observed for a series of chloroethanes. The oscillations are damped in the hard X-ray energy range, but deviations of cross-section ratios from stoichiometry persist, even at high energies. The current findings are supported by theoretical calculations based on a multiple scattering model. The use of soft and tender X-rays provides a more complete picture of the dominant processes accompanying photoionization. Such processes reduce the main photoelectron line intensities by 20-60%. Using both energy ranges enabled us to discern the process of intramolecular inelastic scattering of the outgoing electron, whose significance is otherwise difficult to assess for isolated molecules. This effect relates to the notion of the inelastic mean free path commonly used in photoemission studies of clusters and condensed matter.
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| 45. |
- Travnikova, Oksana, et al.
(författare)
-
Hard-X-Ray-Induced Multistep Ultrafast Dissociation
- 2016
-
Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 116:21
-
Tidskriftsartikel (refereegranskat)abstract
- Creation of deep core holes with very short (tau <= 1 fs) lifetimes triggers a chain of relaxation events leading to extensive nuclear dynamics on a few-femtosecond time scale. Here we demonstrate a general multistep ultrafast dissociation on an example of HCl following Cl 1s -> sigma* excitation. Intermediate states with one or multiple holes in the shallower core electron shells are generated in the course of the decay cascades. The repulsive character and large gradients of the potential energy surfaces of these intermediates enable ultrafast fragmentation after the absorption of a hard x-ray photon.
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| 46. |
- Travnikova, Oksana, et al.
(författare)
-
Photo-induced ultrafast dissociation following deep-core-electron excitation
- 2015
-
Ingår i: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 635
-
Tidskriftsartikel (refereegranskat)abstract
- Creation of deep core holes leads to extensive nuclear dynamics on a few femtosecond timescale despite the very short (tau <= 1 fs) lifetime of such states. This is because the 1st steps of the relaxation processes (i.e. both radiative and non-radiative decays) generate intermediate states with one and multiple holes in core orbitals. As an example, ultrafast dissociation is observed in three well-distinguishable LVV Auger decay channels for HCl following Cl1s ->sigma* excitation.
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| 47. |
- Travnikova, Oksana, et al.
(författare)
-
Selective vibrational excitation in the resonant Auger decay following core-to-pi transitions in N2O
- 2010
-
Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 181:2-3, s. 129-134
-
Tidskriftsartikel (refereegranskat)abstract
- In N2O a detailed study of the vibrational distribution of the (X) over tilde state reached after decay of core-to-pi* excitation of N terminal, N central and 0 1s core levels is reported. We observe a change in the relative intensity of bending versus stretching modes while scanning the photon energy across all three resonances. While this effect is known to be due to the Renner-Teller splitting in the core-excited states, we could derive that the antisymmetric stretching is excited mainly in the decay of the N terminal 1s-to-pi* excitation. An explanation for such selectivity is provided in terms of interplay of vibrational structure on potential energy surfaces of different electronic states involved in the process.
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| 48. |
- Travnikova, Oksana, 1981-
(författare)
-
Structure and Dynamics of Core-Excited Species
- 2008
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis we have performed core-electron spectroscopy studies of gas phase molecular systems starting with smaller diatomic, continuing with triatomic and extending our research to more complex polyatomic ones. We can subdivide the results presented here into two categories: the first one focusing on electronic fine structure and effect of the chemical bonds on molecular core-levels and the other one dealing with nuclear dynamics induced by creation of a core hole. In our research we have mostly used synchrotron radiation based techniques such as X-ray Photoelectron (XPS), X-ray Absorption (XAS), normal and Resonant Auger (AES and RAS, respectively) and Energy-Selected Auger Electron PhotoIon COincidence (ES-AEPICO) spectroscopies.We have demonstrated that resonant Auger spectroscopy can be used to aid interpretation of the features observed in XAS for Rydberg structures in the case of Cl2 and C1s−1π*1 states of allene molecules. The combined use of high-resolution spectroscopy with ab initio calculations can help the interpretation of strongly overlapped spectral features and disentangle their complex profiles. This approach enabled us to determine the differences in the lifetimes for core-hole 2p sublevels of Cl2 which are caused by the presence of the chemical bond. We have shown that contribution in terms of the Mulliken population of valence molecular orbitals is a determining factor for resonant enhancement of different final states and fragmentation patterns reached after resonant Auger decays in N2O.We have also performed a systematic study of the dependence of the C1s resonant Auger kinetic energies on the presence of different substituents in CH3X compounds. For the first time we have studied possible isomerization reaction induced by core excitation of acetylacetone. We could observe a new spectral feature in the resonant Auger decay spectra which we interpreted as a signature of core-excitation-induced keto-enol tautomerism.
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| 49. |
- Velasquez, Nicolas, et al.
(författare)
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Generalization of the post-collision interaction effect from gas-phase to solid-state systems demonstrated in thiophene and its polymers
- 2023
-
Ingår i: Physical Review Research. - : American Physical Society. - 2643-1564. ; 5:1
-
Tidskriftsartikel (refereegranskat)abstract
- We demonstrate experimentally and theoretically the presence of the post-collision interaction (PCI) effect in sulfur KL2,3L2,3 Auger electron spectra measured in the gas-phase thiophene and in solid-state organic polymers: polythiophene (PT) and poly(3-hexylthiophene-2,5-diyl), commonly known as P3HT. PCI manifests itself through a distortion and a blueshift of the normal Auger S KL2,3L2,3 spectrum when S 1s ionization occurs close to the ionization threshold. Our investigation shows that the PCI-induced shift of the Auger spectra is stronger in the solid-state polymers than in the gas-phase organic molecule. Theoretical modeling within the framework of the eikonal approximation provides good agreement with the experimental observations. In a solid medium, two effects influence the interaction between the photoelectron and the Auger electron. In detail, stronger PCI in the polymers is attributed to the photoelectron scattering in the solid, which overcompensates the polarization screening of electron charges which causes a reduction of the interaction. Our paper demonstrates the general nature of the PCI effect occurring in different media.
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| 50. |
- Velasquez, Nicolas, et al.
(författare)
-
X-ray induced ultrafast charge transfer in thiophene-based conjugated polymers controlled by core-hole clock spectroscopy
- 2024
-
Ingår i: Physical Chemistry Chemical Physics. - 1463-9076 .- 1463-9084. ; 26:2, s. 1234-1244
-
Tidskriftsartikel (refereegranskat)abstract
- We explore ultrafast charge transfer (CT) resonantly induced by hard X-ray radiation in organic thiophene-based polymers at the sulfur K-edge. A combination of core-hole clock spectroscopy with real-time propagation time-dependent density functional theory simulations gives an insight into the electron dynamics underlying the CT process. Our method provides control over CT by a selective excitation of a specific resonance in the sulfur atom with monochromatic X-ray radiation. Our combined experimental and theoretical investigation establishes that the dominant mechanism of CT in polymer powders and films consists of electron delocalisation along the polymer chain occurring on the low-femtosecond time scale.
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