1. |
- Allum, Felix, et al.
(author)
-
Coulomb explosion imaging of CH3I and CH2CII photodissociation dynamics
- 2018
-
In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 149:20
-
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. |
- 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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3. |
- 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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4. |
- Carniato, Stéphane, et al.
(author)
-
Resonant X-ray Raman scattering on molecules : A benchmark study on HCl
- 2010
-
In: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 181:2-3, s. 116-120
-
Journal article (peer-reviewed)abstract
- Resonant X-ray Raman scattering is a powerful tool to study molecular dynamics and subtle chemical effects like the molecular field beyond vibrational and lifetime limitations. Using this technique in the tender X-ray region, gas phase HCl is studied as a benchmark molecule for other compounds like freons, which play an important role in physical-chemical properties of the ozone layer of atmosphere.
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5. |
- Céolin, Denis, et al.
(author)
-
Recoil-induced ultrafast molecular rotation probed by dynamical rotational Doppler effect
-
Other publication (other academic/artistic)abstract
- Observing and controlling molecular motion, and in particular rotation,is a fundamental topic in physics and chemistry. In order toinitiate ultrafast rotation, one needs a way to transfer a large angularmomentum to the molecule. As a showcase, this was performedby hard x-ray C1s ionization of carbon monoxide, accompanied byspinning-up the molecule via the recoil “kick” of the emitted fast photoelectron.To visualize this molecular motion, we use the dynamicalrotational Doppler effect and an X-ray “pump-probe” device offeredby nature itself: the recoil-induced ultrafast rotation is probed by subsequentAuger electron emission. The time information in our experimentorigins from the natural delay between the C1s photoionizationinitiating the rotation and the ejection of the Auger electron. From amore general point of view, time-resolved measurements can be performedin two ways: either to vary the "delay" time as in conventionaltime-resolved pump-probe spectroscopy and to use the dynamicsgiven by the system, or to keep constant "delay" time and to manipulatethe dynamics. Since in our experiment we cannot change the delaytime given by the core-hole lifetime $\tau$, we use the second optionand control the rotational speed by changing the kinetic energy of thephotoelectron. The recoil-induced rotational dynamics controlled insuch a way is observed as a photon-energy dependent asymmetryof the Auger lineshape, in full agreement with theory. This asymmetryis explained by a significant change of the molecular orientationduring the core-hole lifetime, which is comparable with the rotationalperiod.
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6. |
- Ceolin, Denis, et al.
(author)
-
Recoil-induced ultrafast molecular rotation probed by dynamical rotational Doppler effect
- 2019
-
In: Proceedings of the National Academy of Sciences of the United States of America. - : NATL ACAD SCIENCES. - 0027-8424 .- 1091-6490. ; 116:11, s. 4877-4882
-
Journal article (peer-reviewed)abstract
- Observing and controlling molecular motion and in particular rotation are fundamental topics in physics and chemistry. To initiate ultrafast rotation, one needs a way to transfer a large angular momentum to the molecule. As a showcase, this was performed by hard X-ray C1s ionization of carbon monoxide accompanied by spinning up the molecule via the recoil "kick" of the emitted fast photoelectron. To visualize this molecular motion, we use the dynamical rotational Doppler effect and an X-ray "pump-probe" device offered by nature itself: the recoil-induced ultrafast rotation is probed by subsequent Auger electron emission. The time information in our experiment originates from the natural delay between the C1s photoionization initiating the rotation and the ejection of the Auger electron. From a more general point of view, time-resolved measurements can be performed in two ways: either to vary the "delay" time as in conventional time-resolved pump-probe spectroscopy and use the dynamics given by the system, or to keep constant delay time and manipulate the dynamics. Since in our experiment we cannot change the delay time given by the core-hole lifetime tau, we use the second option and control the rotational speed by changing the kinetic energy of the photoelectron. The recoil-induced rotational dynamics controlled in such a way is observed as a photon energy-dependent asymmetry of the Auger line shape, in full agreement with theory. This asymmetry is explained by a significant change of the molecular orientation during the core-hole lifetime, which is comparable with the rotational period.
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7. |
- Couto, Rafael C., et al.
(author)
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Anomalously strong two-electron one-photon X-ray decay transitions in CO caused by avoided crossing
- 2016
-
In: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 6
-
Journal article (peer-reviewed)abstract
- The unique opportunity to study and control electron-nuclear quantum dynamics in coupled potentials offered by the resonant inelastic X-ray scattering (RIXS) technique is utilized to unravel an anomalously strong two-electron one-photon transition from core-excited to Rydberg final states in the CO molecule. High-resolution RIXS measurements of CO in the energy region of 12-14 eV are presented and analyzed by means of quantum simulations using the wave packet propagation formalism and ab initio calculations of potential energy curves and transition dipole moments. The very good overall agreement between the experimental results and the theoretical predictions allows an in-depth interpretation of the salient spectral features in terms of Coulomb mixing of "dark" with "bright" final states leading to an effective two-electron one-photon transition. The present work illustrates that the improved spectral resolution of RIXS spectra achievable today may call for more advanced theories than what has been used in the past.
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8. |
- Couto, Rafael C., et al.
(author)
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Coupled electron-nuclear dynamics in resonant 1 sigma -> 2 pi x-ray Raman scattering of CO molecules
- 2016
-
In: Physical Review A. - : American Physical Society. - 2469-9926. ; 93:3
-
Journal article (peer-reviewed)abstract
- We present a detailed experimental-theoretical analysis of O K-edge resonant 1 sigma-2 pi inelastic x-ray scattering (RIXS) from carbon monoxide with unprecedented energy resolution. We employ high-level ab initio calculations to compute the potential energy curves of the states involved in the RIXS process and simulate the measured RIXS spectra using the wave-packet-propagation formalism, including Coulomb coupling in the final-state manifold. The theoretical analysis allows us to explain all the key features of the experimental spectra, including some that were not seen before. First, we clearly show the interference effect between different RIXS channels corresponding to the transition via orthogonal (1)Pi(x) and (1)Pi(y) core-excited states of CO. Second, the RIXS region of 13 eV energy loss presents a triple structure, revealed only by the high-resolution measurement. In previous studies, this region was attributed solely to a valence state. Here we show a strong Coulomb mixing of the Rydberg and valence final states, which opens the forbidden RIXS channels to the "dark" final Rydberg states and drastically changes the RIXS profile. Third, using a combination of high-resolution experiment and high-level theory, we improve the vertical bar 4 sigma(-1)2 pi(1)> final-state potential-energy curve by fitting its bottom part with the experiment. Also, the coupling constants between Rydberg and valence states were refined via comparison with the experiment. Our results illustrate the large potential of the RIXS technique for advanced studies of highly excited states of neutral molecules.
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9. |
- Couto, Rafael C., et al.
(author)
-
Coupled electron-nuclear dynamics in resonant 1σ→2π x-ray Raman scattering of CO molecules
- 2016
-
In: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 93:3
-
Journal article (peer-reviewed)abstract
- We present a detailed experimental-theoretical analysis of O K-edge resonant 1σ-2π inelastic x-ray scattering (RIXS) from carbon monoxide with unprecedented energy resolution. We employ high-level ab initio calculations to compute the potential energy curves of the states involved in the RIXS process and simulate the measured RIXS spectra using the wave-packet-propagation formalism, including Coulomb coupling in the final-state manifold. The theoretical analysis allows us to explain all the key features of the experimental spectra, including some that were not seen before. First, we clearly show the interference effect between different RIXS channels corresponding to the transition via orthogonal Πx1 and Πy1 core-excited states of CO. Second, the RIXS region of 13 eV energy loss presents a triple structure, revealed only by the high-resolution measurement. In previous studies, this region was attributed solely to a valence state. Here we show a strong Coulomb mixing of the Rydberg and valence final states, which opens the forbidden RIXS channels to the "dark" final Rydberg states and drastically changes the RIXS profile. Third, using a combination of high-resolution experiment and high-level theory, we improve the |4σ-12π1) final-state potential-energy curve by fitting its bottom part with the experiment. Also, the coupling constants between Rydberg and valence states were refined via comparison with the experiment. Our results illustrate the large potential of the RIXS technique for advanced studies of highly excited states of neutral molecules.
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10. |
- Goldsztejn, Gildas, et al.
(author)
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Electronic state-lifetime interference in resonant Auger spectra : a tool to disentangle overlapping core-excited states
- 2016
-
In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 18:22, s. 15133-15142
-
Journal article (peer-reviewed)abstract
- We have measured resonant-Auger decay following Cl 1s(-1) excitations in HCl and CH3Cl molecules, and extracted the pseudo-cross sections of different Cl 2p(-2) final states. These cross sections show clear evidence of shake processes as well as contributions of electronic state-lifetime interference (ELI). To describe the spectra we developed a fit approach that takes into account ELI contributions and ultrafast nuclear dynamics in dissociative core-excited states. Using this approach we utilized the ELI contributions to obtain the intensity ratios of the overlapping states Cl 1s(-1)4p pi/1s(-1)4p sigma in HCl and Cl 1s(-1)4pe/1s(-1)4pa(1) in CH3Cl. The experimental value for HCl is compared with theoretical results showing satisfactory agreement.
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11. |
- Guillemin, Renaud, et al.
(author)
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A review of molecular effects in gas-phase KL X-ray emission
- 2013
-
In: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 188, s. 53-61
-
Research review (peer-reviewed)abstract
- The unique capabilities of resonant inelastic X-ray scattering (RIXS) to provide a deep insight into molecular dynamics following core excitation are reviewed here. Characteristic features of molecular X-ray emission are experimentally observed and theoretically interpreted. Some of our most significant results on molecular dynamics following deep core excitation are presented. In particular, we provide several examples of nuclear dynamics on the femtosecond or subfemtosecond time scale; line-narrowing effects related to the quenching of vibrational structure due to parallelism of intermediate and final state curves; anomalous line dispersion across a resonance, which is due to core-hole lifetime effects; spin–orbit-state populations derived from polarized RIXS experiments. We also show how to connect the RIXS results to the general chemical properties of the investigated systems.
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12. |
- Guillemin, Renaud, et al.
(author)
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Angular and dynamical properties in resonant inelastic x-ray scattering : Case study of chlorine-containing molecules
- 2012
-
In: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 86:1
-
Journal article (peer-reviewed)abstract
- Polarization-dependent resonant inelastic x-ray scattering (RIXS) has been shown to be a probe of molecular-field effects on the electronic structure of isolated molecules. In this experimental analysis we explain the linear dichroism observed in Cl 2p polarized RIXS following Cl 1s excitation of a series of chlorofluoromethanes (CF3Cl, CF2Cl2, CFCl3, and CCl4) as due to molecular-field effects, including singlet-triplet exchange. We present an approach to extract directly the 2p inner-shell electronic state populations from the experimental measurements. Using the angular properties of the measured KV emission we also are able to determine the value of the polarization anisotropy parameter beta(p) for each resolved component of the KV emission spectra.
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13. |
- Guillemin, Renaud, et al.
(author)
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Complex decay patterns in atomic core photoionization disentangled by ion-recoil measurements
- 2011
-
In: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 84:6
-
Journal article (peer-reviewed)abstract
- Following core 1s ionization and resonant excitation of argon atoms, we measure the recoil energy of the ions due to momentum conservation during the emission of Auger electrons. We show that such ion momentum spectroscopy can be used to disentangle to some degree complex decay patterns, involving both radiative and nonradiative decays.
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14. |
- Journel, Loïc, et al.
(author)
-
Resonant double Auger decay in carbon K-shell excitation of CO
- 2008
-
In: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 77:4, s. 14-042710
-
Journal article (peer-reviewed)abstract
- We have studied double Auger decay after C 1s→2 photoexcitation in gas phase carbon monoxide. Two distinct processes, namely direct double Auger decay and cascade double Auger decay, are identified and studied in detail using multiple coincidence techniques. Cascade Auger decay is shown to be the overall dominant process. Decay channels involving the dissociation of the molecule followed by autoionization of the oxygen fragments are observed.
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15. |
- Kawerk, Elie, et al.
(author)
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Resonant inelastic x-ray scattering on iso-C2H2Cl2 around the chlorine K-edge : Structural and dynamical aspects
- 2014
-
In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 141:14, s. 144301-
-
Journal article (peer-reviewed)abstract
- We report a theoretical and experimental study of the high resolution resonant K-alpha X-ray emission lines around the chlorine K-edge in gas phase 1,1-dichloroethylene. With the help of ab initio electronic structure calculations and cross section evaluation, we interpret the lowest lying peak in the X-ray absorption and emission spectra. The behavior of the K-alpha emission lines with respect to frequency detuning highlights the existence of femtosecond nuclear dynamics on the dissociative Potential Energy Surface of the first K-shell core-excited state.
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16. |
- Kockert, Hansjochen, et al.
(author)
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UV-induced dissociation of CH2BrI probed by intense femtosecond XUV pulses
- 2022
-
In: JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 55:1
-
Journal article (peer-reviewed)abstract
- The ultraviolet (UV)-induced dissociation and photofragmentation of gas-phase CH2BrI molecules induced by intense femtosecond extreme ultraviolet (XUV) pulses at three different photon energies are studied by multi-mass ion imaging. Using a UV-pump-XUV-probe scheme, charge transfer between highly charged iodine ions and neutral CH2Br radicals produced by C-I bond cleavage is investigated. In earlier charge-transfer studies, the center of mass of the molecules was located along the axis of the bond cleaved by the pump pulse. In the present case of CH2BrI, this is not the case, thus inducing a rotation of the fragment. We discuss the influence of the rotation on the charge transfer process using a classical over-the-barrier model. Our modeling suggests that, despite the fact that the dissociation is slower due to the rotational excitation, the critical interatomic distance for charge transfer is reached faster. Furthermore, we suggest that charge transfer during molecular fragmentation may be modulated in a complex way.
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17. |
- Kushawaha, Rajesh Kumar, et al.
(author)
-
From double-slit interference to structural information in simple hydrocarbons
- 2013
-
In: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 110:38, s. 15201-15206
-
Journal article (peer-reviewed)abstract
- Interferences in coherent emission of photoelectrons from two equivalent atomic centers in a molecule are the microscopic analogies of the celebrated Young's double-slit experiment. By considering inner-valence shell ionization in the series of simple hydrocarbons C2H2, C2H4, and C2H6, we show that double-slit interference is widespread and has built-in quantitative information on geometry, orbital composition, and many-body effects. A theoretical and experimental study is presented over the photon energy range of 70-700 eV. A strong dependence of the oscillation period on the C-C distance is observed, which can be used to determine bond lengths between selected pairs of equivalent atoms with an accuracy of at least 0.01 angstrom. Furthermore, we show that the observed oscillations are directly informative of the nature and atomic composition of the inner-valence molecular orbitals and that observed ratios are quantitative measures of elusive many-body effects. The technique and analysis can be immediately extended to a large class of compounds.
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18. |
- 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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19. |
- Piancastelli, Maria Novella, et al.
(author)
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Core-hole-clock spectroscopies in the tender x-ray domain
- 2014
-
In: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 47:12, s. 124031-
-
Journal article (peer-reviewed)abstract
- The core-hole-clock method to observe dynamical phenomena in molecular photoexcitation on the 1 fs-hundreds-of-attoseconds time scale is illustrated with examples from resonant inelastic x-ray scattering (RIXS) and resonant-Auger-emission experiments on the prototypical CH3Cl system in the tender x-ray domain. In particular, a direct comparison between RIXS and resonant-Auger data allows us to unravel subtle details of nuclear motion and interplay of potential curves of the intermediate and final states reached upon deep-core excitation.
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20. |
- Puettner, Ralph, et al.
(author)
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Direct Observation of Double-Core-Hole Shake-Up States in Photoemission
- 2015
-
In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 114:9
-
Journal article (peer-reviewed)abstract
- Direct measurements of Ar+ 1s(-1)2p(-1)nl double-core-hole shake-up states are reported using conventional single-channel photoemission, offering a new and relatively easy means to study such species. The high-quality results yield accurate energies and lifetimes of the double-core-hole states. Their photoemission spectrum also can be likened to 1s absorption of an exotic argon ion with a 2p core vacancy, providing new information about the spectroscopy of both this unusual ionic state as well as the neutral atom.
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21. |
- Puettner, Ralph, et al.
(author)
-
Si 1s(-1), 2s(-1) and 2p(-1) lifetime broadening of SiX4 (X = F, Cl, Br, CH3) molecules : SiF4 anomalous behaviour reassessed
- 2019
-
In: Physical Chemistry, Chemical Physics - PCCP. - : ROYAL SOC CHEMISTRY. - 1463-9076 .- 1463-9084. ; 21:17, s. 8827-8836
-
Journal article (peer-reviewed)abstract
- The Si 1s(-1), Si 2s(-1), and Si 2p(-1) photoelectron spectra of the SiX4 molecules with X = F, Cl, Br, CH3 were measured. From these spectra the Si 1s(-1) and Si 2s(-1) lifetime broadenings were determined, revealing a significantly larger value for the Si 2s(-1) core hole of SiF4 than for the same core hole of the other molecules of the sequence. This finding is in line with the results of the Si 2p(-1) core holes of a number of SiX4 molecules, with an exceptionally large broadening for SiF4. For the Si 2s(-1) core hole of SiF4 the difference to the other SiX4 molecules can be explained in terms of Interatomic Coulomb Decay (ICD)-like processes. For the Si 2p(-1) core hole of SiF4 the estimated values for the sum of the Intraatomic Auger Electron Decay (IAED) and ICD-like processes are too small to explain the observed linewidth. However, the results of the given discussion render for SiF4 significant contributions from Electron Transfer Mediated Decay (ETMD)-like processes at least plausible. On the grounds of our results, some more molecular systems in which similar processes can be observed are identified.
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22. |
- Simon, Marc, et al.
(author)
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Atomic Auger Doppler effects upon emission of fast photoelectrons
- 2014
-
In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 5, s. 4069-
-
Journal article (peer-reviewed)abstract
- Studies of photoemission processes induced by hard X-rays including production of energetic electrons have become feasible due to recent substantial improvement of instrumentation. Novel dynamical phenomena have become possible to investigate in this new regime. Here we show a significant change in Auger emission following 1s photoionization of neon, which we attribute to the recoil of the Ne ion induced by the emission of a fast photoelectron. Because of the preferential motion of the ionized Ne atoms along two opposite directions, an Auger Doppler shift is revealed, which manifests itself as a gradual broadening and doubling of the Auger spectral features. This Auger Doppler effect should be a general phenomenon in high-energy photoemission of both isolated atoms and molecules, which will have to be taken into account in studies of other recoil effects such as vibrational or rotational recoil in molecules, and may also have consequences in measurements in solids.
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23. |
- 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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24. |
- 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
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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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25. |
- Travnikova, Oksana, et al.
(author)
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Hard-X-Ray-Induced Multistep Ultrafast Dissociation
- 2016
-
In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 116:21
-
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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