| 1. |
- C. Couto, Rafael, 1987-, et al.
(författare)
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Selective gating to vibrational modes through resonant X-ray scattering
- 2017
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Ingår i: Nature Communications. - : Macmillan Publishers Ltd.. - 2041-1723. ; 8, s. 14165-1-14165-7
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Tidskriftsartikel (refereegranskat)abstract
- The dynamics of fragmentation and vibration of molecular systems with a large number of coupled degrees of freedom are key aspects for understanding chemical reactivity and properties. Here we present a resonant inelastic X-ray scattering (RIXS) study to show how it is possible to break down such a complex multidimensional problem into elementary components. Local multimode nuclear wave packets created by X-ray excitation to different core-excited potential energy surfaces (PESs) will act as spatial gates to selectively probe the particular ground-state vibrational modes and, hence, the PES along these modes. We demonstrate this principle by combining ultra-high resolution RIXS measurements for gas-phase water with state-of-the-art simulations.
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| 2. |
- Couto, Rafael C., et al.
(författare)
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Anomalously strong two-electron one-photon X-ray decay transitions in CO caused by avoided crossing
- 2016
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 6
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Tidskriftsartikel (refereegranskat)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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| 3. |
- Couto, Rafael C., et al.
(författare)
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Coupled electron-nuclear dynamics in resonant 1 sigma -> 2 pi x-ray Raman scattering of CO molecules
- 2016
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Ingår i: Physical Review A. - : American Physical Society. - 2469-9926. ; 93:3
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Tidskriftsartikel (refereegranskat)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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| 4. |
- Couto, Rafael C., et al.
(författare)
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Coupled electron-nuclear dynamics in resonant 1σ→2π x-ray Raman scattering of CO molecules
- 2016
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Ingår i: Physical Review A (Atomic, Molecular and Optical Physics). - 1050-2947. ; 93:3
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Tidskriftsartikel (refereegranskat)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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| 5. |
- Ignatova, Nina, 1989-, et al.
(författare)
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Gradual collapse of nuclear wave functions regulated by frequency tuned X-ray scattering
- 2017
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Ingår i: Scientific Reports. - London : Nature Publishing Group. - 2045-2322. ; 7:43891
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Tidskriftsartikel (refereegranskat)abstract
- As is well established, the symmetry breaking by isotope substitution in the water molecule results in localisation of the vibrations along one of the two bonds in the ground state. In this study we find that this localisation may be broken in excited electronic states. Contrary to the ground state, the stretching vibrations of HDO are delocalised in the bound core-excited state in spite of the mass difference between hydrogen and deuterium. The reason for this effect can be traced to the narrow “canyon-like” shape of the potential of the state along the symmetric stretching mode, which dominates over the localisation mass-difference effect. In contrast, the localisation of nuclear motion to one of the HDO bonds is preserved in the dissociative core-excited state . The dynamics of the delocalisation of nuclear motion in these core-excited states is studied using resonant inelastic X-ray scattering of the vibrationally excited HDO molecule. The results shed light on the process of a wave function collapse. After core-excitation into the state of HDO the initial wave packet collapses gradually, rather than instantaneously, to a single vibrational eigenstate.
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| 6. |
- Ignatova, Nina, 1989-, et al.
(författare)
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Infrared-pump–x-ray-probe spectroscopy of vibrationally excited molecules
- 2017
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Ingår i: Physical Review A. - 2469-9926 .- 2469-9934. ; 95:4
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Tidskriftsartikel (refereegranskat)abstract
- We develop a theory of infrared (IR)-pump–x-ray-probe spectroscopy for molecular studies. We illustrate advantages of the proposed scheme by means of numerical simulations employing a vibrational wave packet technique applied to x-ray absorption and resonant inelastic x-ray scattering (RIXS) spectra of the water molecule vibrationally excited by a preceding IR field. The promotion of the vibrationally excited molecule to the dissociative 1a−114a1 and bound 1a−112b2 core-excited states with qualitatively different shapes of the potential energy surfaces creates nuclear wave packets localized along and between the OH bonds, respectively. The projection of these wave packets on the final vibrational states, governed by selection and propensity rules, results in spatial selectivity of RIXS sensitive to the initial vibrationally excited state, which makes it possible to probe selectively the ground state properties along different modes. In addition, we propose to use RIXS as a tool to study x-ray absorption from a selected vibrational level of the ground state when the spectral resolution is sufficiently high to resolve vibrational overtones. The proposed technique has potential applications for advanced mapping of multidimensional potential energy surfaces of ground and core-excited molecular states, for symmetry-resolved spectroscopy, and for steering chemical reactions.
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| 7. |
- Marchenko, T., et al.
(författare)
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Electron Dynamics in the Core-Excited CS2 Molecule Revealed through Resonant Inelastic X-Ray Scattering Spectroscopy
- 2015
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Ingår i: Physical Review X. - 2160-3308. ; 5:3
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Tidskriftsartikel (refereegranskat)abstract
- We present an experimental and theoretical study of resonant inelastic x-ray scattering (RIXS) in the carbon disulphide CS 2 molecule near the sulfur K-absorption edge. We observe a strong evolution of the RIXS spectral profile with the excitation energy tuned below the lowest unoccupied molecular orbital (LUMO) absorption resonance. The reason for this is twofold. Reducing the photon energy in the vicinity of the LUMO absorption resonance leads to a relative suppression of the LUMO contribution with respect to the emission signal from the higher unoccupied molecular orbitals, which results in the modulation of the total RIXS profile. At even larger negative photon-energy detuning from the resonance, the excitation-energy dependence of the RIXS profile is dominated by the onset of electron dynamics triggered by a coherent excitation of multiple electronic states. Furthermore, our study demonstrates that in the hard x-ray regime, localization of the S 1s core hole occurs in CS2 during the RIXS process because of the orientational dephasing of interference between the waves scattering on the two sulfur atoms. Core-hole localization leads to violation of the symmetry selection rules for the electron transitions observed in the spectra.
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| 8. |
- Marchenko, T., et al.
(författare)
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Potential Energy Surface Reconstruction and Lifetime Determination of Molecular Double-Core-Hole States in the Hard X-Ray Regime
- 2017
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Ingår i: Physical Review Letters. - : AMER PHYSICAL SOC. - 0031-9007 .- 1079-7114. ; 119:13
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Tidskriftsartikel (refereegranskat)abstract
- A combination of resonant inelastic x-ray scattering and resonant Auger spectroscopy provides complementary information on the dynamic response of resonantly excited molecules. This is exemplified for CH3I, for which we reconstruct the potential energy surface of the dissociative I 3d(-2) double-core-hole state and determine its lifetime. The proposed method holds a strong potential for monitoring the hard x-ray induced electron and nuclear dynamic response of core-excited molecules containing heavy elements, where ab initio calculations of potential energy surfaces and lifetimes remain challenging.
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| 9. |
- Vaz da Cruz, Vinicius, 1987-, et al.
(författare)
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A study of the water molecule using frequency control over nuclear dynamics in resonant X-ray scattering
- 2017
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 19:30, s. 19573-19589
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Tidskriftsartikel (refereegranskat)abstract
- In this combined theoretical and experimental study we report a full analysis of the resonant inelastic X-ray scattering (RIXS) spectra of H2O, D2O and HDO. We demonstrate that electronically-elastic RIXS has an inherent capability to map the potential energy surface and to perform vibrational analysis of the electronic ground state in multimode systems. We show that the control and selection of vibrational excitation can be performed by tuning the X-ray frequency across core-excited molecular bands and that this is clearly reflected in the RIXS spectra. Using high level ab initio electronic structure and quantum nuclear wave packet calculations together with high resolution RIXS measurements, we discuss in detail the mode coupling, mode localization and anharmonicity in the studied systems.
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| 10. |
- Vaz da Cruz, Vinicius, et al.
(författare)
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A study of the water molecule using frequency control over nuclear dynamics in resonant X-ray scattering
- 2017
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 19:30, s. 19573-19589
-
Tidskriftsartikel (refereegranskat)abstract
- In this combined theoretical and experimental study we report a full analysis of the resonant inelastic X-ray scattering (RIXS) spectra of H2O, D2O and HDO. We demonstrate that electronically-elastic RIXS has an inherent capability to map the potential energy surface and to perform vibrational analysis of the electronic ground state in multimode systems. We show that the control and selection of vibrational excitation can be performed by tuning the X-ray frequency across core-excited molecular bands and that this is clearly reflected in the RIXS spectra. Using high level ab initio electronic structure and quantum nuclear wave packet calculations together with high resolution RIXS measurements, we discuss in detail the mode coupling, mode localization and anharmonicity in the studied systems.
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