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Quantum chemical calculations of multidimensional dynamics probed in resonant inelastic X-ray scattering
Stockholm University, Faculty of Science, Department of Physics.ORCID iD: 0000-0002-4603-2097
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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. 

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University , 2018. , p. 82
Keywords [en]
quantum chemistry, X-ray spectroscopy, RASSCF, density functional theory, ultrafast nuclear dynamics
National Category
Atom and Molecular Physics and Optics
Research subject
Chemical Physics
Identifiers
URN: urn:nbn:se:su:diva-154057ISBN: 978-91-7797-173-3 (print)ISBN: 978-91-7797-174-0 (electronic)OAI: oai:DiVA.org:su-154057DiVA, id: diva2:1190734
Public defence
2018-05-04, sal FP41, hus 1, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.

Available from: 2018-04-11 Created: 2018-03-15 Last updated: 2018-04-04Bibliographically approved
List of papers
1. Selective gating to vibrational modes through resonant X-ray scattering
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2017 (English)In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 8, article id 14165Article in journal (Refereed) Published
Abstract [en]

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.

National Category
Physical Sciences
Research subject
Chemical Physics
Identifiers
urn:nbn:se:su:diva-140323 (URN)10.1038/ncomms14165 (DOI)000392541700001 ()28106058 (PubMedID)
Available from: 2017-03-07 Created: 2017-03-07 Last updated: 2018-03-15Bibliographically approved
2. A study of the water molecule using frequency control over nuclear dynamics in resonant X-ray scattering
Open this publication in new window or tab >>A study of the water molecule using frequency control over nuclear dynamics in resonant X-ray scattering
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2017 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 30, p. 19573-19589Article in journal (Refereed) Published
Abstract [en]

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.

National Category
Physical Sciences
Research subject
Chemical Physics
Identifiers
urn:nbn:se:su:diva-147090 (URN)10.1039/c7cp01215b (DOI)000407053000006 ()28352891 (PubMedID)
Available from: 2017-10-12 Created: 2017-10-12 Last updated: 2018-03-15Bibliographically approved
3. Ultrafast dissociation features in RIXS spectra of the water molecule
Open this publication in new window or tab >>Ultrafast dissociation features in RIXS spectra of the water molecule
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

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.

National Category
Atom and Molecular Physics and Optics
Research subject
Chemical Physics
Identifiers
urn:nbn:se:su:diva-154022 (URN)
Available from: 2018-03-13 Created: 2018-03-13 Last updated: 2018-03-20Bibliographically approved
4. Setting the stage for theoretical X-ray spectra of the H2S molecule with RASPT2 calculations of the energy landscape
Open this publication in new window or tab >>Setting the stage for theoretical X-ray spectra of the H2S molecule with RASPT2 calculations of the energy landscape
(English)Manuscript (preprint) (Other academic)
Abstract [en]

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.

National Category
Atom and Molecular Physics and Optics
Research subject
Chemical Physics
Identifiers
urn:nbn:se:su:diva-154021 (URN)
Available from: 2018-03-13 Created: 2018-03-13 Last updated: 2018-03-20Bibliographically approved
5. Probing hydrogen bonding orbitals: resonant inelastic soft X-ray scattering of aqueous NH3
Open this publication in new window or tab >>Probing hydrogen bonding orbitals: resonant inelastic soft X-ray scattering of aqueous NH3
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2015 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 40, p. 27145-27153Article in journal (Refereed) Published
Abstract [en]

To probe the influence of hydrogen bonding on the electronic structure of ammonia, gas phase and aqueous NH3 have been investigated using soft X-ray absorption (XAS), resonant inelastic soft X-ray scattering (RIXS), and electronic structure calculations including dynamical effects. Strong spectral differences in the XAS scans as well as in the RIXS spectra between gas phase and aqueous NH3 are attributed to orbital mixing with the water orbitals, dipole-dipole interactions, differences in vibronic coupling, and nuclear dynamics on the time-scale of the RIXS process. All of these effects are consequences of hydrogen bonding and the impact of the associated orbitals, demonstrating the power of XAS and RIXS as unique tools to study hydrogen bonding in liquids.

National Category
Physical Sciences
Research subject
Chemical Physics
Identifiers
urn:nbn:se:su:diva-123206 (URN)10.1039/c5cp04898b (DOI)000362679300073 ()
Available from: 2015-11-18 Created: 2015-11-18 Last updated: 2018-03-20Bibliographically approved
6. Theoretical simulations of oxygen K-edge resonant inelastic x-ray scattering of kaolinite
Open this publication in new window or tab >>Theoretical simulations of oxygen K-edge resonant inelastic x-ray scattering of kaolinite
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2017 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 14, article id 144301Article in journal (Refereed) Published
Abstract [en]

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.

National Category
Physical Sciences
Research subject
Chemical Physics
Identifiers
urn:nbn:se:su:diva-143605 (URN)10.1103/PhysRevB.95.144301 (DOI)000399382500002 ()
Available from: 2017-05-31 Created: 2017-05-31 Last updated: 2018-03-15Bibliographically approved

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