| 1. |
- Allum, Felix, et al.
(author)
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Coulomb explosion imaging of CH3I and CH2CII photodissociation dynamics
- 2018
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 149:20
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Journal article (peer-reviewed)abstract
- The photodissociation dynamics of CH3I and CH2CII at 272 nm were investigated by time-resolved Coulomb explosion imaging, with an intense non-resonant 815nmprobe pulse. Fragment ion momenta over a widem/z range were recorded simultaneously by coupling a velocity map imaging spectrometer with a pixel imaging mass spectrometry camera. For both molecules, delay-dependent pump-probe features were assigned to ultraviolet-induced carbon-iodine bond cleavage followed by Coulomb explosion. Multi-mass imaging also allowed the sequential cleavage of both carbon-halogen bonds in CH2ClI to be investigated. Furthermore, delay-dependent relative fragment momenta of a pair of ions were directly determined using recoil-frame covariance analysis. These results are complementary to conventional velocity map imaging experiments and demonstrate the application of time-resolved Coulomb explosion imaging to photoinduced real-time molecular motion.
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| 2. |
- Bao, Zhuo, et al.
(author)
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Detailed Theoretical and Experimental Description of Normal Auger Decay in O2
- 2008
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In: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 41:12, s. 125101-
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Journal article (peer-reviewed)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. |
- Brasse, Felix, et al.
(author)
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Time-resolved inner-shell photoelectron spectroscopy : From a bound molecule to an isolated atom
- 2018
-
In: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - 2469-9926 .- 2469-9934. ; 97:4
-
Journal article (peer-reviewed)abstract
- Due to its element and site specificity, inner-shell photoelectron spectroscopy is a widely used technique to probe the chemical structure of matter. Here, we show that time-resolved inner-shell photoelectron spectroscopy can be employed to observe ultrafast chemical reactions and the electronic response to the nuclear motion with high sensitivity. The ultraviolet dissociation of iodomethane (CH3I) is investigated by ionization above the iodine 4d edge, using time-resolved inner-shell photoelectron and photoion spectroscopy. The dynamics observed in the photoelectron spectra appear earlier and are faster than those seen in the iodine fragments. The experimental results are interpreted using crystal-field and spin-orbit configuration interaction calculations, and demonstrate that time-resolved inner-shell photoelectron spectroscopy is a powerful tool to directly track ultrafast structural and electronic transformations in gas-phase molecules.
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| 4. |
- Burt, Michael, et al.
(author)
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Coulomb-explosion imaging of concurrent CH2BrI photodissociation dynamics
- 2017
-
In: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - 2469-9926 .- 2469-9934. ; 96:4
-
Journal article (peer-reviewed)abstract
- The dynamics following laser-induced molecular photodissociation of gas-phase CH2BrI at 271.6 nm were investigated by time-resolved Coulomb-explosion imaging using intense near-IR femtosecond laser pulses. The observed delay-dependent photofragment momenta reveal that CH2BrI undergoes C-I cleavage, depositing 65.6% of the available energy into internal product states, and that absorption of a second UV photon breaks the C-Br bond of C(H)2Br. Simulations confirm that this mechanism is consistent with previous data recorded at 248 nm, demonstrating the sensitivity of Coulomb-explosion imaging as a real-time probe of chemical dynamics.
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| 5. |
- Ceolin, Denis, et al.
(author)
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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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In: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 184:1-2, s. 24-28
-
Journal article (peer-reviewed)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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| 6. |
- Ceolin, Denis, et al.
(author)
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Site-selective resonant Auger spectroscopy of iso-dichloroethylene at the carbon K-edge
- 2012
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In: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 185:8-9, s. 252-258
-
Journal article (peer-reviewed)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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| 7. |
- 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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| 8. |
- Kockert, Hansjochen, et al.
(author)
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UV-induced dissociation of CH2BrI probed by intense femtosecond XUV pulses
- 2022
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In: JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 55:1
-
Journal article (peer-reviewed)abstract
- The ultraviolet (UV)-induced dissociation and photofragmentation of gas-phase CH2BrI molecules induced by intense femtosecond extreme ultraviolet (XUV) pulses at three different photon energies are studied by multi-mass ion imaging. Using a UV-pump-XUV-probe scheme, charge transfer between highly charged iodine ions and neutral CH2Br radicals produced by C-I bond cleavage is investigated. In earlier charge-transfer studies, the center of mass of the molecules was located along the axis of the bond cleaved by the pump pulse. In the present case of CH2BrI, this is not the case, thus inducing a rotation of the fragment. We discuss the influence of the rotation on the charge transfer process using a classical over-the-barrier model. Our modeling suggests that, despite the fact that the dissociation is slower due to the rotational excitation, the critical interatomic distance for charge transfer is reached faster. Furthermore, we suggest that charge transfer during molecular fragmentation may be modulated in a complex way.
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| 9. |
- Kushawaha, Rajesh K., et al.
(author)
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Multi-slit-type interference in carbon 2s photoionization of polyatomic molecules : from a fundamental effect to structural parameters
- 2019
-
In: Physical Chemistry, Chemical Physics - PCCP. - : ROYAL SOC CHEMISTRY. - 1463-9076 .- 1463-9084. ; 21:25, s. 13600-13610
-
Journal article (peer-reviewed)abstract
- In molecular photoemission, the analogue of the celebrated Young's double slit experiment is coherent electron emission from two equivalent atomic centers, giving rise to an interference pattern. Here multi-slit interference is investigated in inner-valence photoionization of propane, n-butane, isobutane and methyl peroxide. A more complex pattern is observed due to molecular orbital delocalization in polyatomic molecules, blurring the distinction between interference and diffraction. The potential to extract geometrical information is emphasized, as a more powerful extension of the EXAFS technique. Accurate reproduction of experimental features is obtained by simulations at the static Density Functional Theory level.
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| 10. |
- Liu, Xiao-Jing, et al.
(author)
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Einstein-Bohr recoiling double-slit gedanken experiment performed at the molecular level
- 2015
-
In: Nature Photonics. - 1749-4885 .- 1749-4893. ; 9:2, s. 120-125
-
Journal article (peer-reviewed)abstract
- Double-slit experiments illustrate the quintessential proof for wave-particle complementarity. If information is missing about which slit the particle has traversed, the particle, behaving as a wave, passes simultaneously through both slits. This wave-like behaviour and corresponding interference is absent if 'which-slit' information exists. The essence of Einstein-Bohr's debate about wave-particle duality was whether the momentum transfer between a particle and a recoiling slit could mark the path, thus destroying the interference. To measure the recoil of a slit, the slits should move independently. We showcase a materialization of this recoiling double-slit gedanken experiment by resonant X-ray photoemission from molecular oxygen for geometries near equilibrium (coupled slits) and in a dissociative state far away from equilibrium (decoupled slits). Interference is observed in the former case, while the electron momentum transfer quenches the interference in the latter case owing to Doppler labelling of the counter-propagating atomic slits, in full agreement with Bohr's complementarity.
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| 11. |
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| 12. |
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| 13. |
- Miao, Quan, et al.
(author)
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Rotational Doppler Effect : A Probe for Molecular Orbitals Anisotropy
- 2015
-
In: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 6:9, s. 1568-1572
-
Journal article (peer-reviewed)abstract
- The vibrationally resolved X-ray photoelectron spectra of X-2 Sigma(+)(g)(3 sigma(-1)(g)) and B-2 Sigma(+)(u)(2 sigma(-1)(u)) states of N-2(+) were recorded for different photon energies and orientations of the polarization vector. Clear dependencies of the spectral line widths on the X-ray polarization as well as on the symmetry of the final electronic states are observed. Contrary to the translational Doppler, the rotational Doppler broadening is sensitive to the photoelectron emission anisotropy. On the basis of theoretical modeling, we suggest that the different rotational Doppler broadenings observed for gerade and ungerade final states result from a Young's double-slit interference phenomenon.
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| 14. |
- Miron, Catalin, et al.
(author)
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Imaging molecular potentials using ultrahigh-resolution resonant photoemission
- 2012
-
In: Nature Physics. - 1745-2473 .- 1745-2481. ; 8:2, s. 135-138
-
Journal article (peer-reviewed)abstract
- Electron-density distributions and potential-energy surfaces are important for predicting the physical properties and chemical reactivity of molecular systems. Whereas angle-resolved photoelectron spectroscopy enables the reconstruction of molecular-orbital densities of condensed species(1), absorption or traditional photoelectron spectroscopy are widely employed to study molecular potentials of isolated species. However, the information they provide is often limited because not all vibrational substates are excited near the vertical electronic transitions from the ground state. Moreover, many electronic states cannot be observed owing to selection rules or low transition probabilities. In many other cases, the extraction of the potentials is impossible owing to the high densities of overlapping electronic states. Here we use resonant photoemission spectroscopy, where the absence of strict dipole selection rules in Auger decay enables access to a larger number of final states as compared with radiative decay. Furthermore, by populating highly excited vibrational substates in the intermediate core-excited state, it is possible to 'pull out' molecular states that were hidden by overlapping spectral regions before.
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| 15. |
- Miron, Catalin, et al.
(author)
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Site-selective photoemission from delocalized valence shells induced by molecular rotation
- 2014
-
In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 5, s. 3816-
-
Journal article (peer-reviewed)abstract
- Due to the generally delocalized nature of molecular valence orbitals, valence-shell spectroscopies do not usually allow to specifically target a selected atom in a molecule. However, in X-ray electron spectroscopy, the photoelectron momentum is large and the recoil angular momentum transferred to the molecule is larger when the photoelectron is ejected from a light atom compared with a heavy one. This confers an extreme sensitivity of the rotational excitation to the ionization site. Here we show that, indeed, the use of high-energy photons to photoionize valence-shell electrons of hydrogen chloride offers an unexpected way to decrypt the atomic composition of the molecular orbitals due to the rotational dependence of the photoionization profiles. The analysis of the site-specific rotational envelopes allows us to disentangle the effects of the two main mechanisms of rotational excitation, based on angular momentum exchange between the molecule and either the incoming photon or the emitted electron.
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| 16. |
- Piancastelli, Maria Novella, et al.
(author)
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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
-
In: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 40:17, s. 3357-3365
-
Journal article (peer-reviewed)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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| 17. |
- Piancastelli, Maria Novella, et al.
(author)
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Electronic and Geometric Structure of Methyl Oxirane Adsorbed on Si (100) 2 × 1
- 2007
-
In: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 254:1, s. 108-112
-
Journal article (peer-reviewed)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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| 18. |
- Piancastelli, Maria Novella, et al.
(author)
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Electronic Structure of Core-excited and Core-ionized Methyl Oxirane
- 2007
-
In: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 156, s. 259-264
-
Journal article (peer-reviewed)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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| 19. |
- Söderström, Johan, 1978-, et al.
(author)
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Angle-resolved electron spectroscopy of the resonant Auger decay in xenon with meV energy resolution
- 2011
-
In: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 13, s. 073014-
-
Journal article (peer-reviewed)abstract
- The angle-resolved resonant Auger spectrum of Xe is investigated with a record high meV energy resolution in the kinetic energy region of 34.45-39.20 eV at hv = 65.110 eV, corresponding to the resonant excitation of the Auger Xe* 4d(5/2)(-1)6p state. New lines have been observed and assigned in the spectra. The results of previous measurements concerning energies, intensities and angular distribution asymmetry parameters have been refined, complemented and, for some of the lines, corrected.
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| 20. |
- Travnikova, Oksana, et al.
(author)
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A Study of Substituent Effects for Aliphatic CH3-X Compounds by Resonant Auger Spectroscopy
- 2009
-
In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 11:5, s. 826-833
-
Journal article (peer-reviewed)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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| 21. |
- Travnikova, Oksana, et al.
(author)
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Assignment of the L2,3VV normal Auger decay spectrum of Cl-2 by ab initio calculations
- 2009
-
In: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 474:1-3, s. 67-73
-
Journal article (peer-reviewed)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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| 22. |
- Travnikova, Oksana, et al.
(author)
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Circularly Polarized X Rays : Another Probe of Ultrafast Molecular Decay Dynamics
- 2010
-
In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 105:23
-
Journal article (peer-reviewed)abstract
- Dissociative nuclear motion in core-excited molecular states leads to a splitting of the fragment Auger lines: the Auger-Doppler effect. We present here for the first time experimental evidence for an Auger-Doppler effect following F1s -> a(1g)* inner-shell excitation by circularly polarized x rays in SF6. In spite of a uniform distribution of the dissociating S-F bonds near the polarization plane of the light, the intersection between the subpopulation of molecules selected by the core excitation with the cone of dissociation induces a strong anisotropy in the distribution of the S-F bonds that contributes to the scattering profile measured in the polarization plane.
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| 23. |
- Travnikova, Oksana, et al.
(author)
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Disentangling the complex line profiles in the Cl 2p photoelectron spectra of Cl-2
- 2006
-
In: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 426:4-6, s. 452-458
-
Journal article (peer-reviewed)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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| 24. |
- Travnikova, Oksana, et al.
(author)
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Dynamics of core-excited ammonia : disentangling fragmentation pathways by complementary spectroscopic methods
- 2023
-
In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 25:2, s. 1063-1074
-
Journal article (peer-reviewed)abstract
- Fragmentation dynamics of core-excited isolated ammonia molecules is studied by two different and complementary experimental methods, high-resolution resonant Auger spectroscopy and electron energy-selected Auger electron-photoion coincidence spectroscopy (AEPICO). The combined use of these two techniques allows obtaining information on different dissociation patterns, in particular fragmentation before relaxation, often called ultrafast dissociation (UFD), and fragmentation after relaxation. The resonant Auger spectra contain the spectral signature of both molecular and fragment final states, and therefore can provide information on all events occurring during the core-hole lifetime, in particular fragmentation before relaxation. Coincidence measurements allow correlating Auger electrons with ionic fragments from the same molecule, and relating the ionic fragments to specific Auger final electronic states, and yield additional information on which final states are dissociative, and which ionic fragments can be produced in timescales either corresponding to the core-hole lifetime or longer. Furthermore, we show that by the combined use of two complementary experimental techniques we are able to identify more electronic states of the NH2+ fragment with respect to the single one already reported in the literature.
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| 25. |
- Travnikova, Oksana, et al.
(author)
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Energy-Dependent Relative Cross Sections in Carbon 1s Photoionization : Separation of Direct Shake and Inelastic Scattering Effects in Single Molecules
- 2019
-
In: Journal of Physical Chemistry A. - : AMER CHEMICAL SOC. - 1089-5639 .- 1520-5215. ; 123:35, s. 7619-7635
-
Journal article (peer-reviewed)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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| 26. |
- Travnikova, Oksana, et al.
(author)
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Hard-X-Ray-Induced Multistep Ultrafast Dissociation
- 2016
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 116:21
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Journal article (peer-reviewed)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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| 27. |
- Travnikova, Oksana, et al.
(author)
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On Routes to Ultrafast Dissociation of Polyatomic Molecules
- 2013
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In: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 4:14, s. 2361-2366
-
Journal article (peer-reviewed)abstract
- Dissociation pathways for complex polyatomic molecules can sometimes be obscure due to the multitude of degrees of freedom involved. Here, we suggest the description of a dissociation mechanism implying multimode dynamics on the barrierless potential energy surface. The mechanism is elaborated from the X-ray spectroscopic analysis of the ultrafast nuclear motion in core?shell excited molecules. We infer that in large molecules, dissociation pathways are observed to deviate from the two-body dissociation coordinate due to the internal motion of light linkages, which alters dissociation rates and may yield heavy products on very short time scales. The mechanism is exemplified with the case of 1-bromo-2-chloroethane, where the rotation of the C2H4-moiety leads to the dissociation of C?Cl or C?Br bonds in Cl2p or Br3d core-excited states, whose lifetimes last only ?7 fs. Dissociation pathways for complex polyatomic molecules can sometimes be obscure due to the multitude of degrees of freedom involved. Here, we suggest the description of a dissociation mechanism implying multimode dynamics on the barrierless potential energy surface. The mechanism is elaborated from the X-ray spectroscopic analysis of the ultrafast nuclear motion in core?shell excited molecules. We infer that in large molecules, dissociation pathways are observed to deviate from the two-body dissociation coordinate due to the internal motion of light linkages, which alters dissociation rates and may yield heavy products on very short time scales. The mechanism is exemplified with the case of 1-bromo-2-chloroethane, where the rotation of the C2H4-moiety leads to the dissociation of C?Cl or C?Br bonds in Cl2p or Br3d core-excited states, whose lifetimes last only ?7 fs.
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| 28. |
- Travnikova, Oksana, et al.
(author)
-
Photo-induced ultrafast dissociation following deep-core-electron excitation
- 2015
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In: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 635
-
Journal article (peer-reviewed)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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| 29. |
- Travnikova, Oksana, et al.
(author)
-
Selective vibrational excitation in the resonant Auger decay following core-to-pi transitions in N2O
- 2010
-
In: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 181:2-3, s. 129-134
-
Journal article (peer-reviewed)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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| 30. |
- Travnikova, Oksana, 1981-
(author)
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Structure and Dynamics of Core-Excited Species
- 2008
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Doctoral thesis (other academic/artistic)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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| 31. |
- Travnikova, Oksana, et al.
(author)
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The ESCA molecule-Historical remarks and new results
- 2012
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In: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 185:8-9, s. 191-197
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Journal article (peer-reviewed)abstract
- The C is photoelectron spectrum of ethyl trifluoroacetate (CF3-CO-O-CH2-CH3), also known as the 'ESCA molecule', is the most illustrative showcase of chemical shifts in photoelectron spectroscopy. The binding energies of the four carbon atoms of this molecule spread over more than 8 eV with energy separations ranging from 1.7 to 3.1 eV owing to different chemical environments and hence different charge states of these atoms. The paper discusses history and importance of this spectrum in the field of photoelectron spectroscopy starting from the time of invention of the ESCA technique. The main focus of the paper is a 'revisit' of this spectrum using the most modern experimental and computational tools. Large geometrical changes, different for each ionization site, and the presence of two conformers of ethyl trifluoroacetate influence the spectral lineshapes of all four C 1s lines. These effects are carefully modeled by theory and investigated in the experimental spectrum.
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| 32. |
- Velasquez, Nicolas, et al.
(author)
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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
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In: Physical Review Research. - : American Physical Society. - 2643-1564. ; 5:1
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Journal article (peer-reviewed)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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| 33. |
- Velasquez, Nicolas, et al.
(author)
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X-ray induced ultrafast charge transfer in thiophene-based conjugated polymers controlled by core-hole clock spectroscopy
- 2024
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In: Physical Chemistry Chemical Physics. - 1463-9076 .- 1463-9084. ; 26:2, s. 1234-1244
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Journal article (peer-reviewed)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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