| 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. |
- da Cruz, Vinicius Vaz, et al.
(författare)
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Anomalous polarization dependence in vibrationally resolved resonant inelastic x-ray scattering of H2O
- 2018
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Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : American Physical Society. - 2469-9926 .- 2469-9934. ; 98:1
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Tidskriftsartikel (refereegranskat)abstract
- It is well established that different electronic channels, in resonant inelastic x-ray scattering (RIXS), display different polarization dependences due to different orientations of their corresponding transition dipole moments in the molecular frame. However, this effect does not influence the vibrational progression in the Franck-Condon approximation. We have found that the transition dipole moments of core excitation and deexcitation experience ultrafast rotation during dissociation in the intermediate core-excited state. This rotation makes the vibrational progression in RIXS sensitive to the polarization of the x-ray photons. We study the water molecule, in which the effect is expressed in RIXS through the dissociative core-excited state where the vibrational scattering anisotropy is accompanied also by violation of parity selection rules for the vibrations.
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| 3. |
- da Cruz, Vinicius Vaz, et al.
(författare)
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Probing hydrogen bond strength in liquid water by resonant inelastic X-ray scattering
- 2019
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- Local probes of the electronic ground state are essential for understanding hydrogen bonding in aqueous environments. When tuned to the dissociative core-excited state at the O1s pre-edge of water, resonant inelastic X-ray scattering back to the electronic ground state exhibits a long vibrational progression due to ultrafast nuclear dynamics. We show how the coherent evolution of the OH bonds around the core-excited oxygen provides access to high vibrational levels in liquid water. The OH bonds stretch into the long-range part of the potential energy curve, which makes the X-ray probe more sensitive than infra-red spectroscopy to the local environment. We exploit this property to effectively probe hydrogen bond strength via the distribution of intramolecular OH potentials derived from measurements. In contrast, the dynamical splitting in the spectral feature of the lowest valence-excited state arises from the short-range part of the OH potential curve and is rather insensitive to hydrogen bonding.
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| 4. |
- Eckert, Sebastian, et al.
(författare)
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One-dimensional cuts through multidimensional potential-energy surfaces by tunable x rays
- 2018
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Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : AMER PHYSICAL SOC. - 2469-9926 .- 2469-9934. ; 97:5
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Tidskriftsartikel (refereegranskat)abstract
- The concept of the potential-energy surface (PES) and directional reaction coordinates is the backbone of our description of chemical reaction mechanisms. Although the eigenenergies of the nuclear Hamiltonian uniquely link a PES to its spectrum, this information is in general experimentally inaccessible in large polyatomic systems. This is due to (near) degenerate rovibrational levels across the parameter space of all degrees of freedom, which effectively forms a pseudospectrum given by the centers of gravity of groups of close-lying vibrational levels. We show here that resonant inelastic x-ray scattering (RIXS) constitutes an ideal probe for revealing one-dimensional cuts through the ground-state PES of molecular systems, even far away from the equilibrium geometry, where the independent-mode picture is broken. We strictly link the center of gravity of close-lying vibrational peaks in RIXS to a pseudospectrum which is shown to coincide with the eigenvalues of an effective one-dimensional Hamiltonian along the propagation coordinate of the core-excited wave packet. This concept, combined with directional and site selectivity of the core-excited states, allows us to experimentally extract cuts through the ground-state PES along three complementary directions for the showcase H2O molecule.
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| 5. |
- Ertan, Emelie, 1988-
(författare)
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Ab initio simulations of vibrational and electronic structure evaluated against K-edge resonant inelastic X-ray scattering
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The work of this thesis is focused on investigation of electronic and molecular structure and dynamics a molecular species in solutions and minerals in relation to resonant inelastic X-ray scattering (RIXS). The studies have been carried out by means of quantum chemistry calculations using density functional theory (DFT) and multi-configurational methods and quantum dynamics simulations using wave packet dynamics and ab initio molecular dynamics. By applications of these computational tools, I have studied the ultra-fast core-excited state dynamics and the RIXS process. With theoretical spectrum simulations, we can analyse the vibrational information of RIXS.The aim of these investigations is to probe the local electronic structure of ammonia and the hydroxyl group and their chemical interactions with the environment, e.g. hydrogen bonding, in liquid and solid state molecular systems. In Paper I, DFT calculations and wave packet dynamics has been used to simulate the O K-edge X-ray absorption (XAS) spectra and RIXS spectra to investigate the local vibrational structure of the hydroxyl groups of the kaolinite crystal. In Paper II, the N K-edge XAS, XES and RIXS spectra are simulated by application of DFT and multi-configurational methods combined with ab initio molecular dynamics with the aim to study the hydrogen bonding environment of aqueous NH3.
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| 6. |
- Ertan, Emelie, 1988-
(författare)
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Quantum chemical calculations of multidimensional dynamics probed in resonant inelastic X-ray scattering
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is devoted to the theoretical study of the dynamical processes induced by light-matter interactions in molecules and molecular systems. To this end, the multidimensional nuclear dynamics probed in resonant inelastic X-ray scattering (RIXS) of small molecules, exemplified by H2O (g) and H2S (g), as well as more complex molecular systems, exemplified by NH3 (aq) and kaolinite clay, are modelled. The computational methodology consists of a combination of ab initio quantum chemistry calculations, quantum nuclear wave packet dynamics and in certain cases molecular dynamics modelling. This approach is used to simulate K-edge RIXS spectra and the theoretical results are evaluated against experimental measurements.Specifically, the vibrational profile for decay back to the electronic ground state of the H2O molecule displays a vibrational selectivity introduced by the dynamics in the core-excited state. Simulation of the inelastic decay channel to the electronic |1b1-1,4a11> valence-excited state shows that the splitting of the spectral profile arises from the contribution of decay in the OH fragment. The character of the S1s-1 and S2p-1 core-excited states of the H2S molecule has been investigated and distinct similarities and differences with the H2O molecule have been identified. RIXS has also been used as a probe of the hydrogen bonding environment in aqueous ammonia and by detailed analysis of the valence orbitals of NH3 and water, the spectral profiles are explained. Finally, it is shown that vibrations of weakly hydrogen bonding OH are excited in RIXS decay to the electronic ground state in kaolinite.
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| 7. |
- Ertan, Emelie, et al.
(författare)
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Setting the stage for theoretical x-ray spectra of the H2S molecule with multi-configurational quantum chemical calculations of the energy landscape
- 2020
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 152:9
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Tidskriftsartikel (refereegranskat)abstract
- In the H2S molecule, the interplay between different core levels can be investigated in great detail in relation to x-ray spectroscopy, which requires a theory for interpretation. Hence, valence and core excitations into the two antibonding molecular orbitals of the H2S molecule have been calculated within a multi-configurational wave function framework. Scanning along the S-H stretching coordinates, we derive potential energy surfaces and transition dipole moments involving the ground state and core and valence excited states. Both valence excitations and the S1s(-1) and S2p(-1) core excitations show pairs of dissociative and bound electronic states. These pairs of states are nearly degenerate in H2S at the ground state geometry. The close degeneracy together with conical intersections makes H2S an interesting target for x-ray spectroscopy involving ultra-fast dissociation influenced by non-adiabatic transitions and interference. For future investigations with x-ray absorption spectroscopy (XAS) and resonant inelastic x-ray scattering (RIXS), it is valuable to compare H2S with the water molecule, which exhibits state-selective gating to different vibrational modes [R. C. Couto et al., Nat. Commun. 8, 14165 (2017)] in its well-separated O1s(-1) core excited states. The dense manifolds of the S2p(-1) core excited states will complicate the analysis of K-alpha edge RIXS, but dynamical effects could be evaluated through detuning and by comparing with L edge XAS. In L edge RIXS, the dynamical effects will be more pronounced due to the longer lifetime of the S2p(-1) core excited states compared to the S1s(-1) core excited states.
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| 8. |
- Ertan, Emelie, et al.
(författare)
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Setting the stage for theoretical X-ray spectra of the H2S molecule with RASPT2 calculations of the energy landscape
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Electronic valence- and core-excitations into the anti-bonding orbitals of the H2S molecule have been calculated within a multi-configurational wave-function framework (RASPT2). Potential energy surfaces and transition dipole moments have been derived in two dimensions for the S-H stretching coordinates. The |S1s-1, 6a11> and |S1s-1, 3b21> core-excited states in H2S are nearly degenerate along the symmetric stretching coordinate, for which we have identified two conical intersections. The small energy splitting of the S1s-1 core-excited states at equilibrium geometry arise from an avoided crossing at broken symmetry. Compared to the water molecule, which exhibit state-selective gating to different vibrational modes [Nat. Commun. 8 14165 (2017)] in its well-separated O1s-1 core-excited states, we expect a strong coupling between the close-lying |S1s-1, 6a11> and |S1s-1, 3b21> states. This could lead to dissociative dynamics observable in K-edge RIXS. The S2p-1 core-excited states form two dense manifolds of spin-orbit coupled states, which can be schematically characterised as bound |S2p-1,3b21> and dissociative |S2p-1,6a11> states. We identify three conical intersections in the singlet and triplet states along the symmetric stretching coordinate. Mapping the molecular singlet and triplet states to the atomic dissociation limit reveals a symmetry selection rule, leading to an off-set of the 1|3a1-1,6a11> state relative to the other S2p-1 core-excited states. The dense manifolds of S2p-1 core-excited states will complicate the analysis of Kα-edge RIXS, but dynamical effects could be evaluated through detuning and in comparison to L-edge XAS. In L-edge RIXS, the dynamical effects well be more pronounced due to a longer life-time of the S2p-1 core-excited states compared to the S1s-1 core-excited states.
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| 9. |
- Ertan, Emelie, et al.
(författare)
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Theoretical simulations of oxygen K-edge resonant inelastic x-ray scattering of kaolinite
- 2017
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 95:14
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Tidskriftsartikel (refereegranskat)abstract
- Near-edge x-ray absorption fine structure (NEXAFS) and resonant inelastic x-ray scattering (RIXS) measurements at the oxygen K edge were combined with theoretical spectrum simulations, based on periodic density functional theory and nuclear quantum dynamics, to investigate the electronic structure and chemical bonding in kaolinite Al2Si2O5(OH)(4). We simulated NEXAFS spectra of all crystallographically inequivalent oxygen atoms in the crystal and RIXS spectra of the hydroxyl groups. Detailed insight into the ground-state potential energy surface of the electronic states involved in the RIXS process were accessed by analyzing the vibrational excitations, induced by the core excitation, in quasielastic scattering back to the electronic ground state. In particular, we find that the NEXAFS pre-edge is dominated by features related to OH groups within the silica and alumina sheets, and that the vibrational progression in RIXS can be used to selectively probe vibrational modes of this subclass of OH groups. The signal is dominated by the OH stretching mode, but also other lower vibrational degrees of freedom, mainly hindered rotational modes, contribute to the RIXS signal.
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| 10. |
- Ertan, Emelie, et al.
(författare)
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Ultrafast dissociation features in RIXS spectra of the water molecule
- 2018
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - 1463-9076 .- 1463-9084.
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Tidskriftsartikel (refereegranskat)abstract
- In this combined theoretical and experimental study we report on an analysis of the resonant inelastic X-ray scattering spectra (RIXS) of gas phase water via the lowest dissociative core-excited state |1sO-14a11〉. We focus on the spectral feature near the dissociation limit of the electronic ground state. We show that the narrow atomic-like peak consists of the overlapping contribution from the RIXS channels back to the ground state and to the first valence excited state |1b1-14a11〉 of the molecule. The spectral feature has signatures of ultrafast dissociation (UFD) in the core-excited state, as we show by means of ab initio calculations and time-dependent nuclear wave packet simulations. We show that the electronically elastic RIXS channel gives substantial contribution to the atomic-like resonance due to the strong bond length dependence of the magnitude and orientation of the transition dipole moment. By studying the RIXS for an excitation energy scan over the core-excited state resonance, we can understand and single out the molecular and atomic-like contributions in the decay to the lowest valence-excited state. Our study is complemented by a theoretical discussion of RIXS in the case of the isotope substituted water (HDO and D2O) where the nuclear dynamics is significantly affected by the heavier fragments' mass.
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