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Coupled electron-nuclear dynamics in inelastic X-ray scattering
KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. (Theoretical Chemistry and Biology)ORCID iD: 0000-0003-4020-0923
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This Thesis is devoted to theoretical and experimental studies of resonant inelastic X-ray scattering (RIXS) of carbon monoxide and water molecules. Using state-of-the-art ab initio electronic structure calculations and a time-dependent wave packet formalism, we make a complete analysis of the experimental RIXS spectra of the two molecular systems. In the CO RIXS analysis, we are able to reproduce the RIXS experiment with an excellent accuracy. Interference between different RIXS channels corresponding to the scattering via orthogonal molecular orbitals in the core-excited state of CO is described. We show the complete breakdown of the Born-Oppenheimer approximation in the region where forbidden final Rydberg states are mixed with a valence allowed final state. Here we explain the formation of a spectral feature which was attributed to a single state in previous studies. Moreover, through an experimental-theoretical combination, we improve the minimum of the valence E’Π excited state potential, along with the coupling constant between two Rydberg states. We developed a new theoretical approach to describe triatomic molecules through the wave packet propagation formalism to study the water system, which reproduces with high accuracy the vibrational structure of the high-resolution experimental quasi-elastic RIXS spectra. We demonstrate that due to the vibrational mode coupling and anharmonicity of the ground and core-excited potential energy surfaces, different core-excited states in RIXS can be used as gates to probe different vibrational dynamics and to map the ground state potential. Isotopic substitution is investigated by theoretical simulations and important dynamical features are discussed, especially for the dissociative core-excited state, where a so-called “atomic” peak is formed. We show the strong potential of high-resolution RIXS experiments combined with high-level theoretical simulations for advanced studies of highly excited molecular states.

Place, publisher, year, edition, pages
Stockholm, Sweden: KTH Royal Institute of Technology, 2016. , 87 p.
Series
TRITA-BIO-Report, ISSN 1654-2312 ; 2016:10
Keyword [en]
X-ray spectroscopy, resonant inelastic X-ray scattering, water, carbon monoxide
National Category
Theoretical Chemistry
Research subject
Theoretical Chemistry and Biology
Identifiers
URN: urn:nbn:se:kth:diva-186530ISBN: 978-91-7595-988-7OAI: oai:DiVA.org:kth-186530DiVA: diva2:927657
Public defence
2016-06-08, FB53, AlbaNova University Center, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Knut and Alice Wallenberg Foundation, KAW-2013.0020
Note

QC 20160516

Available from: 2016-05-16 Created: 2016-05-12 Last updated: 2016-05-16Bibliographically approved
List of papers
1. Anomalously strong two-electron one-photon X-ray decay transitions in CO caused by avoided crossing
Open this publication in new window or tab >>Anomalously strong two-electron one-photon X-ray decay transitions in CO caused by avoided crossing
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2016 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, 20947Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Nature Publishing Group, 2016
National Category
Engineering and Technology Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-183187 (URN)10.1038/srep20947 (DOI)000369829300001 ()26860458 (PubMedID)2-s2.0-84957534824 (ScopusID)
Funder
Swedish National Infrastructure for Computing (SNIC), SNIC 2015/1-69; SNIC 023/07-18Swedish Research CouncilKnut and Alice Wallenberg Foundation, KAW-2013.0020
Note

QC 20160303

Available from: 2016-03-03 Created: 2016-03-03 Last updated: 2016-09-21Bibliographically approved
2. Coupled electron-nuclear dynamics in resonant 1 sigma -> 2 pi x-ray Raman scattering of CO molecules
Open this publication in new window or tab >>Coupled electron-nuclear dynamics in resonant 1 sigma -> 2 pi x-ray Raman scattering of CO molecules
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2016 (English)In: Physical Review A, ISSN 2469-9926, Vol. 93, no 3, 032510Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
American Physical Society, 2016
Keyword
Spectra, Excitation, Photoemission, Emission, Model
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-185360 (URN)10.1103/PhysRevA.93.032510 (DOI)000372399100006 ()2-s2.0-84961724217 (ScopusID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation, KAW-2013.0020
Note

QC 20160420

Available from: 2016-04-20 Created: 2016-04-18 Last updated: 2016-05-16Bibliographically approved
3. Selective gating to vibrational modes through resonant X-ray scattering
Open this publication in new window or tab >>Selective gating to vibrational modes through resonant X-ray scattering
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

AbstractIn this study we use the gas-phase water to demonstrate how dierent intermediate core-excitedstates in ultra-high resolution resonant inelastic X-ray scattering (RIXS) may act as selective gatesto specic vibrational modes by means of spatially selective nuclear dynamics in the core-excitedstate. The alignment of the wave packet along the OH bonds and between the bonds for the |1a1-14a11>  and |1a1-12b21> states, respectively, allows to probe vibrational states aligned preferen-tially along these directions. The combination of experiment with state-of-the-art ab initio calcula-tions allows to explain this selectivity and observed propensity rule with a detailed analysis of thepotential energy surfaces (PESs) of the ground and core-excited states and by making use of thetime-dependent wave packet picture. We show that the RIXS technique makes it possible to probeextended regions of the ground state PES along each internal degree of freedom and to study theregime of normal-to-local mode transitions for symmetric molecules A2B. In particular, the abilityto visualize the transition from the normal to the local mode regimes by means of RIXS may beimportant for mapping chemical reactions.

Keyword
water, resonant elastic x-ray scattering, vibrational modes, RIXS
National Category
Atom and Molecular Physics and Optics
Research subject
Theoretical Chemistry and Biology
Identifiers
urn:nbn:se:kth:diva-187011 (URN)
Funder
Knut and Alice Wallenberg Foundation, KAW-2013.0020
Note

QCR 20160517

Available from: 2016-05-16 Created: 2016-05-16 Last updated: 2016-05-17Bibliographically approved
4. Resonant elastic X-ray scattering in H2O, D2O and HDO with vibrational resolution: mode filtering, mode localization, and potential energy surface mapping
Open this publication in new window or tab >>Resonant elastic X-ray scattering in H2O, D2O and HDO with vibrational resolution: mode filtering, mode localization, and potential energy surface mapping
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Using gas-phase water as demonstration case we show in this combined experimental and theoretical study that there is an inherent capability of resonant elastic X-rays cattering (REXS) spectroscopy to map the potential energy surface and vibrational modes of the ground state and that such mapping is complementarity different for X-ray scattering through different resonant core-excited states. REXS can thus be used as a filter for separate excitation of particular vibrational motions in the ground state, making possible a unique and better mapping of the potential energy for each normal mode. We show that the use of frequency detuning and isotope substitution can act as additional tools to fine tune information about the ground state, in both cases by altering the wave packet dynamics in the core-excited state. Several details about mode coupling, mode localization, anharmonicity and energy positioning of high vibrational quanta could be revealed. Some ramifications of the findings with respect to general molecules and comparison to other spectroscopic techniques are briefly mentioned.

National Category
Atom and Molecular Physics and Optics
Research subject
Theoretical Chemistry and Biology
Identifiers
urn:nbn:se:kth:diva-187012 (URN)
Funder
Knut and Alice Wallenberg Foundation, KAW-2013.0020
Note

QC 20160516

Available from: 2016-05-16 Created: 2016-05-16 Last updated: 2016-05-16Bibliographically approved

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