| 1. |
- Bueno, AM, et al.
(author)
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Influence of chemical bonds on the lifetime of the molecular-field-split 2p levels in H2S
- 2003
-
In: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 67, s. 22714:1-7
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Journal article (peer-reviewed)abstract
- Different lifetime broadenings in molecular-field-split 2p core levels in H2S are predicted theoretically and are identified in an experimental investigation of the S 2p Auger electron spectrum. The measurements were performed for the transition to the vibrationally resolved X(1)A(1) ground state of H2S2+. The lifetimes of the 3e(1/2) and 5e(1/2) levels of the 2p ionized molecule are found to be 64 and 74 meV, respectively. This unambiguous determination of the lifetime difference of 10+/-1 meV is only possible as the 4e(1/2)-->X(1)A(1)(2b(1)(-2)) decay channel that overlaps the 5e(1/2)-->X(1)A(1)(2b(1)(-2)) channel is practically suppressed in Auger decay in H2S. The lifetime difference is confirmed by ab initio calculations. A theoretical analysis shows that it results from the mutual orientation of the core hole in the intermediate states and the valence electron density in the sulfur 3p orbitals. Both are strongly influenced by the chemical bond. Thus the observed effect is the direct result of a fundamental property of molecular electronic structure.
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| 2. |
- Lindgren, Andreas, et al.
(author)
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Core localization and sigma( *) delocalization in the O 1s core-excited sulfur dioxide molecule.
- 2008
-
In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 128:11
-
Journal article (peer-reviewed)abstract
- Electron-ion-ion coincidence measurements of sulfur dioxide at discrete resonances near the O 1s ionization edge are reported. The spectra are analyzed using a model based upon molecular symmetry and on the geometry of the molecule. We find clear evidence for molecular alignment that can be ascribed to symmetry properties of the ground and core-excited states. Configuration interaction (CI) calculations indicate geometry changes in accord with the measured spectra. For the SO(2) molecule, however, we find that the localized core hole does not produce measurable evidence for valence localization, since the transition dipole moment is not parallel to a breaking sigma(*) O-S bond, in contrast to the case of ozone. The dissociation behavior based upon the CI calculations using symmetry-broken orbitals while fixing a localized core-hole site is found to be nearly equivalent to that using symmetry-adapted orbitals. This implies that the core-localization effect is not strong enough to localize the sigma(*) valence orbital.
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| 3. |
- Mocellin, Alexandra, et al.
(author)
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Site selective dissociation upon core ionization of ozone
- 2007
-
In: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 435:4-6, s. 214-218
-
Journal article (peer-reviewed)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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| 4. |
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| 5. |
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| 6. |
- Ahluwalia, T. S., et al.
(author)
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Genome-wide association study of circulating interleukin 6 levels identifies novel loci
- 2021
-
In: Human molecular genetics. - : Oxford University Press (OUP). - 0964-6906 .- 1460-2083. ; 30:5, s. 393-409
-
Journal article (peer-reviewed)abstract
- Interleukin 6 (IL-6) is a multifunctional cytokine with both pro- and anti-inflammatory properties with a heritability estimate of up to 61%. The circulating levels of IL-6 in blood have been associated with an increased risk of complex disease pathogenesis. We conducted a two-staged, discovery and replication meta genome-wide association study (GWAS) of circulating serum IL-6 levels comprising up to 67428 (n(discovery)=52654 and n(replication)=14774) individuals of European ancestry. The inverse variance fixed effects based discovery meta-analysis, followed by replication led to the identification of two independent loci, IL1F10/IL1RN rs6734238 on chromosome (Chr) 2q14, (P-combined=1.8x10(-11)), HLA-DRB1/DRB5 rs660895 on Chr6p21 (P-combined=1.5x10(-10)) in the combined meta-analyses of all samples. We also replicated the IL6R rs4537545 locus on Chr1q21 (P-combined=1.2x10(-122)). Our study identifies novel loci for circulating IL-6 levels uncovering new immunological and inflammatory pathways that may influence IL-6 pathobiology.
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| 7. |
- Baev, A., et al.
(author)
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Geometrical information on core-excited states obtained from interference quenching of vibrational states in resonant x-ray photoemission
- 2003
-
In: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 67:2
-
Journal article (peer-reviewed)abstract
- An interference quenching of the m=1 final state vibrational line in the resonant Auger decay of N 1s-->pi(*) core-excited N-2 is observed and analyzed. The intensity ratio between the m=1 and m=0 vibrational levels of the X (2)Sigma(g)(+) final state shows a surprising nonmonotonic variation as a function of frequency detuning, going through a minimum with a complete suppression of m=1. We have developed a simple model which indicates a linear relation between the value of the detuning frequency for this minimum and the equilibrium bond distance of the core-excited state. This implies the possibility of determining the equilibrium bond distances for core-excited states to a high degree of accuracy. Simultaneously with the simple model we present a strict theory of the studied effect. This strict theory allows us to explore the accuracy of determining the bond length of the core-excited state from resonant Auger spectra. We obtain a weak influence of the core-hole lifetime on the determined bond length, whereas the number of intermediate vibrational states accounted for in the numerical simulations seems to be quite important.
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| 8. |
- Burmeister, F., et al.
(author)
-
A study of the inner-valence ionization region in HCl and DCl
- 2004
-
In: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 37:6, s. 1173-1183
-
Journal article (peer-reviewed)abstract
- An in-depth photoionization study of the inner-valence electrons in HCl and DCl has been performed using synchrotron radiation. A series of photoelectron spectra of HCl were obtained at a resolution of 23 meV over the binding energy range 25-30.5 eV at various excitation energies and at two different electron collection angles relative to the plane of polarization of the undulator radiation. In addition, photoelectron spectra of DCl were recorded at two different excitation energies. These spectra were compared directly with the threshold photoelectron spectra of HCl and DCl that were recorded previously under similar resolution conditions (similar to30 meV). This comparative study reveals new information on the nature of the numerous band systems observed in this binding energy region. In addition, we present the experimental confirmation of the theoretical prediction given by Andersson et al (2001 Phys. Rev. A 65 012705) that a vibrational progression showing interference structure would appear in the main inner-valence ionization band in the photoelectron spectrum of DCl at a resolution of 10 meV.
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| 9. |
- Burmeister, Florian, et al.
(author)
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Description and performance of an electron-ion coincidence TOF spectrometer used at the Brazilian synchrotron facility LNLS
- 2010
-
In: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 180:1-3, s. 6-13
-
Journal article (peer-reviewed)abstract
- This paper reports the characteristics and performance of a Time-of-Flight Mass Spectrometer (TOF-MS) for coincidence measurements between electrons and ions that has been developed jointly in Sweden and Brazil. The spectrometer, used for studies of inner-shell photoexcitation of molecules in the gas-phase, has been optimized by implementing ion and electron lenses to allow the use of relatively small diameter detectors. Simulations were performed to understand the lens performance and they show that ions (electrons) could be collected without angular discrimination with a maximum kinetic energy up to ten (two) times higher than without the lens actions. A rotary vacuum chamber allows the spectrometer axis to be positioned at different angles relative to the polarization vector of the excitation beam. An important characteristic of the apparatus is that the acquisition setup allows a multi-hit capability with 1 ns resolution. Hereby, Photoelectron-Photoion-Photoion Coincidence (PEPIPICO) measurements can be performed on molecules containing two or more atoms of equal mass. A method to obtain experimental detection efficiencies of a single ion and one of one, two or three electrons has been developed. A systematic study of the interaction region has been performed to determine the shape of the photon and gas beams. Measurements on molecular nitrogen demonstrate the spectrometer's ability to resolve fragments with the same charge to mass ratio arriving within only a few ns. Simulations and experimental results of fragmentation of two singly charged cation nitrogen atoms agree, confirming that the spectrometer performance is well understood. (C) 2010 Elsevier B.V. All rights reserved.
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| 10. |
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| 11. |
- Bässler, M., et al.
(author)
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Soft x-ray undulator beam line 1411 at MAX-II for gases, liquids and solid samples
- 1999
-
In: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048. ; 101-103, s. 953-957
-
Journal article (peer-reviewed)abstract
- We report on the build-up of the new undulator beam line 1411 at the third-generation synchrotron radiation facility MAX II in Lund, Sweden. This beam line is based on an upgraded version of the modified SX700-monochromator and the end station which were installed previously at beam line 51 at MAX I. The end station is equipped with a rotatable Scienta hemispherical electron-analyser making angle-resolved high resolution electron spectroscopy possible for various kinds of samples. The beam line performance will be considerably improved on MAX II due to a new undulator and the superior light source properties, e.g. the small vertical electron beam size. Undulator spectra have been measured and estimates of the photon flux at the experiment and the expected energy resolution are presented. The parameters for a new refocusing mirror were defined by ray tracing using the beam waist of the undulator. The beam line length was extended by 1 m to offer additional space for exchangeable experimental chambers.
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| 12. |
- Couto, Rafael Carvalho, et al.
(author)
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Breaking inversion symmetry by protonation : Experimental and theoretical NEXAFS study of the diazynium ion, N2H
- 2021
-
In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 23:32, s. 17166-17176
-
Journal article (peer-reviewed)abstract
- As an example of symmetry breaking in NEXAFS spectra of protonated species we present a high resolution NEXAFS spectrum of protonated dinitrogen, the diazynium ion N2H+. By ab initio calculations we show that the spectrum consists of a superposition of two nitrogen 1s absorption spectra, each including a π∗ band, and a nitrogen 1s to H+ charge transfer band followed by a weak irregular progression of high energy excitations. Calculations also show that, as an effect of symmetry breaking by protonation, the π∗ transitions are separated by 0.23 eV, only slightly exceeding the difference in the corresponding dark (symmetry forbidden) and bright (symmetry allowed) core excitations of neutral N2. By DFT and calculations and vibrational analysis, the complex π∗ excitation band of N2H+ is understood as due to the superposition of the significantly different vibrational progressions of excitations from terminal and central nitrogen atoms, both leading to bent final state geometries. We also show computationally that the electronic structure of the charge transfer excitation smoothly depends on the nitrogen-proton distance and that there is a clear extension of the spectra going from infinity to close nitrogen-proton distance where fine structures show some, although not fully detailed, similarities. An interesting feature of partial localization of the nitrogen core orbitals, with a strong, non-monotonous, variation with nitrogen-proton distance could be highlighted. Specific effects could be unraveled when comparing molecular cation NEXAFS spectra, as represented by recently recorded spectra of N2+ and CO+, and spectra of protonated molecules as represented here by the N2H+ ion. Both types containing rich physical effects not represented in NEXAFS of neutral molecules because of the positive charge, whereas protonation also breaks the symmetry. The effect of the protonation on dinitrogen can be separated in charge, which extends the high-energy part of the spectrum, and symmetry-breaking, which is most clearly seen in the low-energy π∗ transition.
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| 13. |
- Couto, Rafael Carvalho, et al.
(author)
-
The carbon and oxygen K-edge NEXAFS spectra of CO
- 2020
-
In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 22:28, s. 16215-16223
-
Journal article (peer-reviewed)abstract
- We present and analyze high resolution near edge X-ray absorption fine structure (NEXAFS) spectra of CO+ at the carbon and oxygen K-edges. The spectra show a wealth of features that appear very differently at the two K-edges. The analysis of these features can be divided into three parts; (i) repopulation transition to the open shell orbital – here the C(1s) or O(1s) to 5σ transition, where the normal core hole state is reached from a different initial state and different interaction than in X-ray photoelectron spectroscopy; (ii) spin coupled split valence bands corresponding to C(1s) or O(1s) to π* transitions; (iii) remainder weak and long progressions towards the double ionization potentials containing a manifold of peaks. These parts, none of which has correspondence in NEXAFS spectra of neutral molecules, are dictated by the localization of the singly occupied 5σ orbital, adding a dimension of chemistry to the ionic NEXAFS technique.
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| 14. |
- da Silva, DA, et al.
(author)
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Vibronic coupling in the ground and excited states of the naphthalene cation
- 2004
-
In: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1359-7345 .- 1364-548X. ; :15, s. 1702-1703
-
Journal article (peer-reviewed)abstract
- The hole - vibrational coupling in naphthalene is studied using high-resolution gas-phase photoelectron spectroscopy and density functional theory calculations (DFT), and a remarkable increase of the coupling with low-frequency vibrations is observed in the excited states.
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| 15. |
- de Jong, Michel P, et al.
(author)
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Femtosecond charge transfer in assemblies of discotic liquid crystals
- 2008
-
In: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 112:40, s. 15784-15790
-
Journal article (peer-reviewed)abstract
- The electronic coupling strength within columns of discotic liquid crystals is investigated using core-level resonant photoemission spectroscopy. Coexisting well-ordered and disordered regions are identified in thin films of tetra-alkoxy-substituted phthalocyanines with the aid of near edge X-ray absorption fine structure and photoelectron spectroscopies. These different regions are used to derive a lower limit for the intermolecular charge transfer bandwidth within the framework of the core-hole clock principle. We find average charge transfer times on the order of a few femtoseconds, that is, significantly faster than the C(ls) core-hole lifetime, which indicates a surprisingly strong electronic coupling between the phthalocyanine units as compared to what is expected from the charge transport characteristics of this material. © 2008 American Chemical Society.
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| 16. |
- de Jong, Michel P, 1970-, et al.
(author)
-
Orbital-specific dynamic charge transfer from Fe(II)-tetraphenylporphyrin molecules to molybdenum disulfide substrates
- 2005
-
In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 72:3, s. 35448-
-
Journal article (peer-reviewed)abstract
- Orbital-specific femtosecond charge transfer dynamics between Fe(II)-tetraphenylporphyrin molecules and semimetallic molybdenum disulfide substrates is investigated using core-level resonant photoemission spectroscopy. The electronic coupling to the substrate and the efficiency of charge transport across the interface is found to be different for the individual molecular electronic subsystems. In particular, electrons excited at the phenyl substituents are transferred within 3–6 fs, while hopping from the porphyrin ring is slower than 30 fs.
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| 17. |
- Eland, John H. D., 1941, et al.
(author)
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Carbon dioxide ion dissociations after inner shell excitation and ionization: The origin of site-specific effects
- 2014
-
In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 140:18
-
Journal article (peer-reviewed)abstract
- Multi-coincidence experiments with detection of both electrons and ions from decay of core-excited and core-ionized states of CO2 confirm that O-2(+) is formed specifically in Auger decay from the C1s-pi* and O1s-pi* resonances. Molecular rearrangement occurs by bending in the resonant states, and O-2(+) is produced by both single and double Auger decay. It is suggested that electron capture by C+ after partial dissociation in the doubly ionized core of excited CO2+, formed by shake-up in spectator resonant Auger decay, accounts for high kinetic energy and high internal energy in some C + O-2(+) fragments. (C) 2014 AIP Publishing LLC.
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| 18. |
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| 19. |
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| 20. |
- Feifel, R., et al.
(author)
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Interference quenching of nu('')=1 vibrational line in resonant photoemission of N-2 : A possibility to obtain geometrical information on the core-excited state
- 2002
-
In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 89:10
-
Journal article (peer-reviewed)abstract
- An interference quenching of the nu=1 vibrational line in the resonant Auger decay of N 1s-->pi(*) core-excited N-2 is observed and analyzed. The intensity ratio between the nu=1 and nu=0 vibrational levels of the X(2)Sigma(g)(+) final state shows a surprising nonmonotonous variation as a function of frequency detuning, going through a minimum with a complete suppression of nu=1. We have developed a simple model which shows a linear relation between the value of the detuning frequency for this minimum and the equilibrium bond distance R-c(0) of the core-excited state. A new way is thus established of determining the equilibrium bond distance for the core-excited state with a precision deltaR(c)(0)<10(-3) Angstrom.
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| 21. |
- Feifel, Raimund, et al.
(author)
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Interference Quenching of v
- 2002
-
In: Physical Review Letters. ; 89:10, s. 103002-1
-
Journal article (peer-reviewed)
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| 22. |
- Feifel, R., et al.
(author)
-
Profile of resonant photoelectron spectra versus the spectral function width and photon frequency detuning
- 2004
-
In: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 70:3
-
Journal article (peer-reviewed)abstract
- The outermost, singly ionized valence state of N-2, the X (2)Sigma(g)(+) state, is investigated in detail as a function of the photon frequency bandwidth for core excitation to the N 1s-->pi(*) resonance, where the photon frequency is tuned in between the first two vibrational levels of this bound intermediate electronic state. We find a strong, nontrivial dependence of the resulting resonant photoemission spectral profile on the monochromator function width and the frequency of its peak position. For narrow bandwidth excitation we observe a well resolved vibrational fine structure in the final electron spectrum, which for somewhat broader bandwidths gets smeared out into a continuous structure. For even broader monochromator bandwidths, it converts again into a well resolved vibrational progression. In addition, spectral features appearing below the adiabatic transition energy of the ground state of N-2(+) are observed for broadband excitation. A model taking into account the interplay of the partial scattering cross section with the spectral function is presented and applied to the X (2)Sigma(g)(+) final state of N-2(+).
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| 23. |
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| 24. |
- Feifel, R., et al.
(author)
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Role of stray light in the formation of high-resolution resonant photoelectron spectra : an experimental and theoretical study of N-2
- 2004
-
In: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 134:1, s. 49-65
-
Journal article (peer-reviewed)abstract
- We show that the undular stray light, diffusely scattered by the optical system of a synchrotron beamline, can play an important role in the formation of high-resolution resonant photoelectron (RPE) spectra. The influence of the stray light is mediated through the Stokes doubling effect, with the Lorentzian tail of the spectral function being replaced by a more complicated form. This effect is shown to appear in the high-resolution resonant photoelectron spectrum of the N-2 molecule in which the spectral shape of the non-Raman (NR) bands differs qualitatively for the A(2)Pi(u) and X(2)Sigma(g)(+) final states. A particularly large enhancement of the non-Raman Stokes line is observed for the A-state while the picture is inverted for the X-state where the non-Raman band is suppressed. It is shown that the resonant photoemission profile is affected by two qualitatively different detunings, the detuning of the monochromatized line relative to the photoabsorption line and the detuning of the undulator harmonic relative to the same reference line. The experimental data show that the relative intensity of the non-Raman line strongly depends on the tuning of the undulator harmonic with respect to the selected monochromator bandpass, leading to a strong decrease of the Stokes line intensity for certain undulator detunings. A clear red-shift asymmetry for the decrease in the Stokes line intensity is observed when the monochromator line is detuned towards negative photon frequencies, whereas the picture is reverted for the situation of a positively detuned monochromator line. The results show the necessity to control the stray light and to investigate both the Raman and non-Raman contributions to the spectral profiles in order to avoid misinterpretation and in order to make full use of the information available in resonant photoemission spectra of molecules.
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| 25. |
- Feifel, R., et al.
(author)
-
X-ray absorption and resonant Auger spectroscopy of O(2) in the vicinity of the O 1s ->sigma* resonance : Experiment and theory
- 2008
-
In: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 128:6
-
Journal article (peer-reviewed)abstract
- We report on an experimental and theoretical investigation of x-ray absorption and resonant Auger electron spectra of gas phase O(2) recorded in the vicinity of the O 1s ->sigma* excitation region. Our investigation shows that core excitation takes place in a region with multiple crossings of potential energy curves of the excited states. We find a complete breakdown of the diabatic picture for this part of the x-ray absorption spectrum, which allows us to assign an hitherto unexplained fine structure in this spectral region. The experimental Auger data reveal an extended vibrational progression, for the outermost singly ionized X (2)Pi(g) final state, which exhibits strong changes in spectral shape within a short range of photon energy detuning (0 eV>Omega>-0.7 eV). To explain the experimental resonant Auger electron spectra, we use a mixed adiabatic/diabatic picture selecting crossing points according to the strength of the electronic coupling. Reasonable agreement is found between experiment and theory even though the nonadiabatic couplings are neglected. The resonant Auger electron scattering, which is essentially due to decay from dissociative core-excited states, is accompanied by strong lifetime-vibrational and intermediate electronic state interferences as well as an interference with the direct photoionization channel. The overall agreement between the experimental Auger spectra and the calculated spectra supports the mixed diabatic/adiabatic picture.
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| 26. |
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| 27. |
- Fouda, Adam, et al.
(author)
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Influence of Selective Carbon 1s Excitation on Auger–Meitner Decay in the ESCA Molecule
- 2024
-
In: Journal of Physical Chemistry Letters. - 1948-7185. ; 15:16, s. 4286-4293
-
Journal article (peer-reviewed)abstract
- Two-dimensional spectral mapping is used to visualize how resonant Auger–Meitner spectra are influenced by the site of the initial core–electron excitation and the symmetry of the core-excited state in the trifluoroethyl acetate molecule (ESCA). We observe a significant enhancement of electron yield for excitation of the COO 1s → π* and CF3 1s → σ* resonances unlike excitation at resonances involving the CH3 and CH2 sites. The CF3 1s → π* and CF3 1s → σ* resonance spectra are very different from each other, with the latter populating most valence states equally. Two complementary electronic structure calculations for the photoelectron cross section and Auger–Meitner intensity are shown to effectively reproduce the site- and state-selective nature of the resonant enhancement features. The site of the core–electron excitation and the respective final state hole locality increase the sensistivity of the photoelectron signal at specific functional group sites. This showcases resonant Auger–Meitner decay as a potentially powerful tool for selectively probing structural changes at specific functional group sites of polyatomic molecules.
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| 28. |
- Friedlein, Rainer, et al.
(author)
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Electronic structure of conjugated polymers and interfaces in polymer-based electronics
- 2003
-
In: Synthetic Metals (Proceedings of the International Conference on Science and Technology of Synthetic Metals). - 0379-6779. ; 135:1-3, s. 275-277
-
Conference paper (peer-reviewed)abstract
- The electronic structure of conjugated polymers and interfaces in polymer-based electronics were analyzed. Fine structure were observed in the region of the first resonance with pi-final state symmetry, between 284.1 eV and 285.8 eV. The electronic transitions from the non-dispersed C(1s) level to specific parts of the unoccupied band structure were generated. It was found that for a dispersing valence band, in the presence of a core-hole, a given photon energy corresponded to an excitation into a state with a distinct wave vectors.
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| 29. |
- Friedlein, Rainer, et al.
(author)
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Role of electronic localization and charge-vibrational coupling in resonant photoelectron spectra of polymers : Application to poly(para-phenylenevinylene)
- 2004
-
In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 69:12
-
Journal article (peer-reviewed)abstract
- A combination of x-ray absorption and resonant photoemission (RPE) spectroscopy has been used to study the electronic structure of the one-dimensional conjugated polymer poly (para-phenylenevinylene) in nonordered (as prepared) thin films. The dispersion of RPE features for the decay to localized and delocalized bands are qualitatively different. A theory for band dispersion of RPE in polymers is given, showing the important roles of electronic state localization and vibrational (phonon) excitations for the character of the dispersion.
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| 30. |
- Ganguly, Smita, et al.
(author)
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The origin of enhanced O2+ production from photoionized CO2 clusters
- 2022
-
In: Communications Chemistry. - 2399-3669.
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Journal article (peer-reviewed)abstract
- CO2-rich planetary atmospheres are continuously exposed to ionising radiation driving major photochemical processes. In the Martian atmosphere, CO2 clusters are predicted to exist at high altitudes motivating a deeper understanding of their photochemistry. In this joint experimental-theoretical study, we investigate the photoreactions of CO2 clusters (≤2 nm) induced by soft X-ray ionisation. We observe dramatically enhanced production of O2- from photoionized CO2 clusters compared to the case of the isolated molecule and identify two relevant reactions. Using quantum chemistry calculations and multi-coincidence mass spectrometry, we pinpoint the origin of this enhancement: A size-dependent structural transition of the clusters from a covalently bonded arrangement to a weakly bonded polyhedral geometry that activates an exothermic reaction producing O+2. Our results unambiguously demonstrate that the photochemistry of small clusters/particles will likely have a strong influence on the ion balance in atmospheres.
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| 31. |
- Gisselbrecht, Mathieu, et al.
(author)
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Charge migration and decay of doubly charged ammonia clusters
- 2012
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In: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 388:2, s. 022112-
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Journal article (peer-reviewed)abstract
- The photo-fragmentation of ammonia molecular clusters ionized with soft x-rays is studied for photon energies near the N-1s threshold. The fragmentation is studied with a 3D momentum mass spectrometer to access the energy and angular correlations between fragments. By choosing the cluster sizes below or above the critical size of stable dication, we investigate the coulomb explosion dynamics and the interplay between charge delocalization and mobility of molecules in the clusters.
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| 32. |
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| 33. |
- Inhester, Ludger, et al.
(author)
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Chemical Understanding of the Limited Site-Specificity in Molecular Inner-Shell Photofragmentation
- 2018
-
In: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 9:5, s. 1156-1163
-
Journal article (peer-reviewed)abstract
- In many cases fragmentation of molecules upon inner-shell ionization is very unspecific with respect to the initially localized ionization site. Often this finding is interpreted in terms of an equilibration of internal energy into vibrational degrees of freedom after Auger decay. We investigate the X-ray photofragmentation of ethyl trifluoroacetate upon core electron ionization at environmentally distinct carbon sites using photoelectron-photoion-photoion coincidence measurements and ab initio electronic structure calculations. For all four carbon ionization sites, the Auger decay weakens the same bonds and transfers the two charges to opposite ends of the molecule, which leads to a rapid dissociation into three fragments, followed by further fragmentation steps. The lack of site specificity is attributed to the character of the dicationic electronic states after Auger decay instead of a fast equilibration of internal energy.
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| 34. |
- Iwan, Bianca
(author)
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Creating and Probing Extreme States of Materials : From Gases and Clusters to Biosamples and Solids
- 2012
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Doctoral thesis (other academic/artistic)abstract
- Free-electron lasers provide high intensity pulses with femtosecond duration and are ideal tools in the investigation of ultrafast processes in materials. Illumination of any material with such pulses creates extreme conditions that drive the sample far from equilibrium and rapidly convert it into high temperature plasma. The dynamics of this transition is not fully understood and the main goal of this thesis is to further our knowledge in this area.We exposed a variety of materials to X-ray pulses of intensities from 1013 to above 1017 W/cm2. We found that the temporal evolution of the resulting plasmas depends strongly on the wavelength and pulse intensity, as well as on material related parameters, such as size, density, and composition.In experiments on atomic and molecular clusters, we find that cluster size and sample composition influence the destruction pathway. In small clusters a rapid Coulomb explosion takes place while larger clusters undergo a hydrodynamic expansion. We have characterized this transition in methane clusters and discovered a strong isotope effect that promotes the acceleration of deuterium ions relative to hydrogen. Our results also show that ions escaping from exploding xenon clusters are accelerated to several keV energies.Virus particles represent a transition between hetero-nuclear clusters and complex biological materials. We injected single mimivirus particles into the pulse train of an X-ray laser, and recorded coherent diffraction images simultaneously with the fragmentation patterns of the individual particles. We used these results to test theoretical damage models. Correlation between the diffraction patterns and sample fragmentation shows how damage develops after the intense pulse has left the sample.Moving from sub-micron objects to bulk materials gave rise to new phenomena. Our experiments with high-intensity X-ray pulses on bulk, metallic samples show the development of a transient X-ray transparency. We also describe the saturation of photoabsorption during ablation of vanadium and niobium samples.Photon science with extremely strong X-ray pulses is in its infancy today and will require much more effort to gain more knowledge. The work described in this thesis represents some of the first results in this area.
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| 35. |
- J Doherty, Walter, et al.
(author)
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Selective hydrogen bond disruption in adenine monolayer films by reaction with water
- 2009
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In: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048. ; 174:1-3, s. 107-109
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Journal article (peer-reviewed)abstract
- High-resolution X-ray photoelectron spectroscopy of two-dimensional films of adenine on a highly oriented pyrolitic graphite [0 0 0 1] surface reveal bonding changes induced by exposure to water. The hydrogen-bond interactions between adenine molecules were replaced by adenine-water hydrogen bonds in a stepwise pattern. This reaction destroyed the film network and changed the chemical state of the nitrogen sites. The reaction with water molecules affected both the donor and acceptor states of the oxygen atoms, as compared to those in water. (C) 2009 Elsevier B.V. All rights reserved.
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| 36. |
- Kitajima, M., et al.
(author)
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Angle-resolved photoion yield and resonant Auger spectroscopy for the doubly excited Rydberg states above the C 1s threshold of CO
- 2008
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In: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 78:3, s. 033422-
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Journal article (peer-reviewed)abstract
- Doubly excited core-hole states of carbon monoxide in the photon energy region of 300-305 eV, i.e., directly above the C 1s ionization threshold, have been studied using both angle-resolved ion-yield and high-resolution resonant Auger spectroscopies. The leading configurations of the most prominent doubly excited Rydberg states are assigned by careful analysis of the ion-yield spectra and the final-state spectra to C 1s(-1) (5 sigma(-1)2 pi S-1=1) 3s sigma (v'=0,1,2), C 1s(-1) (5 sigma(-1)2 pi S-1=0) 3s sigma (v'=0,1,2), and C 1s(-1) (5 sigma(-1)2 pi S-1=1) 4s sigma (v'=0,1), which can only be populated via a conjugate shake-up process. Analysis of the resonant Auger spectra provides an assignment of several two-hole-one-electron (2h-1e) final states.
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| 37. |
- Kitajima, M., et al.
(author)
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Doppler effect in resonant photoemission from SF6 : Correlation between doppler profile and auger emission anisotropy
- 2003
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 91:21
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Journal article (peer-reviewed)abstract
- Fragmentation of the SF6 molecule upon F 1s excitation has been studied by resonant photoemission. The F atomiclike Auger line exhibits the characteristic Doppler profile that depends on the direction of the photoelectron momentum relative to the polarization vector of the radiation as well as on the photon energy. The measured Doppler profiles are analyzed by the model simulation that takes account of the anisotropy of the Auger emission in the molecular frame. The Auger anisotropy extracted from the data decreases with an increase in the F-SF5 internuclear distance.
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| 38. |
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| 39. |
- Le Guen, K., et al.
(author)
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H2S ultrafast dissociation probed by energy-selected resonant Auger electron–ion coincidence measurements
- 2007
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 127:11, s. 114315-
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Journal article (peer-reviewed)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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| 40. |
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| 41. |
- Lindblad, Rebecka, Dr, 1984-, et al.
(author)
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Experimental and theoretical near-edge x-ray-absorption fine-structure studies of NO
- 2022
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In: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : American Physical Society. - 2469-9926 .- 2469-9934. ; 106:4
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Journal article (peer-reviewed)abstract
- Experimental near-edge x-ray-absorption fine-structure (NEXAFS) spectra of the nitrosonium NO+ ion are presented and theoretically analyzed. While neutral NO has an open shell, the cation is a closed-shell species, which for NEXAFS leads to the simplicity of a closed-shell spectrum. Compared to neutral NO, the electrons in the cation experience a stronger Coulomb potential, which introduces a shift of the ionization potential towards higher energies, a depletion of intensity in a large interval above the pi* resonance, and a shift of the sigma* resonance from the continuum to below the ionization threshold. NEXAFS features at the nitrogen and oxygen K edges of NO+ are compared, as well as NEXAFS features at the nitrogen edges of the isoelectronic closed-shell species NO+, N2, and N2H+.
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| 42. |
- Lindblad, Rebecka, et al.
(author)
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Experimental and theoretical near-edge x-ray-absorption fine-structure studies of NO
- 2022
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In: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : American Physical Society (APS). - 2469-9926 .- 2469-9934. ; 106:4
-
Journal article (peer-reviewed)abstract
- Experimental near-edge x-ray-absorption fine-structure (NEXAFS) spectra of the nitrosonium NO+ ion are presented and theoretically analyzed. While neutral NO has an open shell, the cation is a closed-shell species, which for NEXAFS leads to the simplicity of a closed-shell spectrum. Compared to neutral NO, the electrons in the cation experience a stronger Coulomb potential, which introduces a shift of the ionization potential towards higher energies, a depletion of intensity in a large interval above the pi* resonance, and a shift of the sigma* resonance from the continuum to below the ionization threshold. NEXAFS features at the nitrogen and oxygen K edges of NO+ are compared, as well as NEXAFS features at the nitrogen edges of the isoelectronic closed-shell species NO+, N2, and N2H+.
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| 43. |
- Minkov, Ivaylo, et al.
(author)
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Core-excitations of naphthalene : Vibrational structure versus chemical shifts
- 2004
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 121:12, s. 5733-5739
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Journal article (peer-reviewed)abstract
- The initial state chemical shifts and vibrational fine structure of core excitations of naphthalene were analyzed using high-resolution x-ray photoelectron emission (XPS) and near-edge x-ray absorption fine structure (NEXAFS) spectra. The carbon atoms at peripheral sites were found to experience a small chemical shift and exhibit similar charge-vibrational coupling. The C-H stretching modes provide significant contributions to overall shape of spectra in the XPS spectra. The results show that vibrational fine structure dominates by particular C-C stretching modes, and in XPS of C2 and C3 sites also by high-energy C-H stretching modes.
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| 44. |
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| 45. |
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| 46. |
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| 47. |
- Oghbaie, Shabnam, et al.
(author)
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Dissociation of cyclopropane in double ionization continuum
- 2017
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In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 19:30, s. 19631-19639
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Journal article (peer-reviewed)abstract
- Dissociative double photoionization of cyclopropane is studied in the inner-valence region using tunable synchrotron radiation. With the aid of ab initio quantum chemical calculations the energies of dication states and their favoured fragmentation pathways are determined. These are compared to the experimental appearance energies of two-body fragmentation processes and to the kinetic energy released upon dissociation. Photon energy dependent state-selective dissociation in the 25-35 eV range is found. Calculations of dissociation pathways suggest that cyclopropane ring-deformation is selectively triggered at certain photon energies. The calculations suggest that initial ring deformation essentially determines the population of different dication states that function as gateways for particular dissociation channels. The measurements show that stepwise ionization processes populate dissociative 3e'(-2) states via ring-opening and Jahn-Teller active states at photon energies below the double-ionization threshold. For energies above the double-ionization threshold the kinematics indicate that double ionization takes place predominantly within the Franck-Condon region populating 3e'(-1) 1e ''(-1) states.
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| 48. |
- Oghbaiee, Shabnam, et al.
(author)
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Site-dependent nuclear dynamics in core-excited butadiene
- 2022
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In: Physical chemistry chemical physics : PCCP. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 24:47, s. 28825-28830
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Journal article (peer-reviewed)abstract
- Symmetry breaking and competition between electronic decay and nuclear dynamics are major factors determining whether the memory of the initial core-hole localisation in a molecule is retained long enough to affect fragmentation. We investigate the fate of core holes localised at different sites in the free 1,3 trans butadiene molecule by using synchrotron radiation to selectively excite core electrons from different C 1s sites to π* orbitals. Fragmentation involving bonds localised at the site of the core hole provides clear evidence for preferential bond breaking for a core hole located at the terminal carbon site, while the signature of localisation is weak for a vacancy on the central carbon site. The origin of this difference is attributed to out-of-plane vibrations, and statistical evaporation of protons for vacancies located at the central carbon sites.
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| 49. |
- Oostenrijk, Bart, et al.
(author)
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Fission of charged nano-hydrated ammonia clusters - microscopic insights into the nucleation processes
- 2019
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In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 21:46, s. 25749-25762
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Journal article (peer-reviewed)abstract
- While largely studied on the macroscopic scale, the dynamics leading to nucleation and fission processes in atmospheric aerosols are still poorly understood at the molecular level. Here, we present a joint experimental-theoretical study of a model system consisting of hydrogen-bonded ammonia and water molecules. Experimentally, the clusters were produced via adiabatic co-expansion. Double ionization ionic products were prepared using synchrotron radiation and analyzed with coincidence mass- and 3D momentum spectroscopy. Calculations were carried out using ab initio molecular dynamics to understand the fragmentation within the first similar to 500 fs. Further exploration of the potential energy surfaces was performed at a DFT level of theory to gain information on the energetics of the processes. Water was identified as an efficient nano-droplet stabilizer, and is found to have a significant effect even at low water content. On the molecular level, the stabilizing role of water can be related to an increase in the dissociation energy between ammonia molecules and the water enriched environment at the cluster surface. Furthermore, our results support the role of ammonium as a charge carrier in the solution, preferentially bound to surrounding ammonia molecules, which can influence the atmospheric nucleation process.
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| 50. |
- Oostenrijk, Bart, et al.
(author)
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The role of charge and proton transfer in fragmentation of hydrogen-bonded nanosystems : The breakup of ammonia clusters upon single photon multi-ionization
- 2018
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In: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 20:2, s. 932-940
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Journal article (peer-reviewed)abstract
- The charge and proton dynamics in hydrogen-bonded networks are investigated using ammonia as a model system. The fragmentation dynamics of medium-sized clusters (1-2 nm) upon single photon multi-ionization is studied, by analyzing the momenta of small ionic fragments. The observed fragmentation pattern of the doubly- and triply-charged clusters reveals a spatial anisotropy of emission between fragments (back-to-back). Protonated fragments exhibit a distinct kinematic correlation, indicating a delay between ionization and fragmentation (fission). The different kinematics observed for channels containing protonated and unprotonated species provides possible insights into the prime mechanisms of charge and proton transfer, as well as proton hopping, in such a nanoscale system.
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