| 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. |
- Brasse, Felix, et al.
(author)
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Time-resolved inner-shell photoelectron spectroscopy : From a bound molecule to an isolated atom
- 2018
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In: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - 2469-9926 .- 2469-9934. ; 97:4
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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
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In: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - 2469-9926 .- 2469-9934. ; 96:4
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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. |
- Céolin, Denis, et al.
(author)
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Recoil-induced ultrafast molecular rotation probed by dynamical rotational Doppler effect
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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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| 5. |
- Ceolin, Denis, et al.
(author)
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Recoil-induced ultrafast molecular rotation probed by dynamical rotational Doppler effect
- 2019
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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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| 6. |
- 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
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In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 18:22, s. 15133-15142
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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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| 7. |
- Guillemin, Renaud, et al.
(author)
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A review of molecular effects in gas-phase KL X-ray emission
- 2013
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In: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 188, s. 53-61
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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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| 8. |
- Guillemin, Renaud, et al.
(author)
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Complex decay patterns in atomic core photoionization disentangled by ion-recoil measurements
- 2011
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In: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 84:6
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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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| 9. |
- Inhester, Ludger, et al.
(author)
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Chemical Understanding of the Limited Site-Specificity in Molecular Inner-Shell Photofragmentation
- 2018
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In: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 9:5, s. 1156-1163
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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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| 10. |
- 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
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 141:14, s. 144301-
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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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