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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: 978-91-7595-988-7 (print)OAI: 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 (Scopus ID)
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 (Scopus ID)
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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2017 (English)In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 8, 14165-1-14165-7 p.Article in journal, Letter (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.

Place, publisher, year, edition, pages
Macmillan Publishers Ltd., 2017
Keyword
water, resonant inelastic x-ray scattering, vibrational modes, RIXS
National Category
Atom and Molecular Physics and Optics Theoretical Chemistry
Research subject
Theoretical Chemistry and Biology
Identifiers
urn:nbn:se:kth:diva-187011 (URN)10.1038/ncomms14165 (DOI)000392541700001 ()2-s2.0-85009990586 (Scopus ID)
Funder
Knut and Alice Wallenberg Foundation, KAW-2013.0020Carl Tryggers foundation , CTS 15:266Carl Tryggers foundation , CTS 14:355Swedish Research Council, C0334701Swedish Research Council, 2015-03781Swedish Research Council, 2015-03956Swedish Research Council, 2015-04510EU, Horizon 2020, 669531 EDAX
Note

QC 20170123

Available from: 2016-05-16 Created: 2016-05-16 Last updated: 2017-03-09Bibliographically approved
4. 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 1463-9084Article 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.

Keyword
RIXS, water, quantum dynamics, x-ray
National Category
Atom and Molecular Physics and Optics
Research subject
Theoretical Chemistry and Biology
Identifiers
urn:nbn:se:kth:diva-187012 (URN)10.1039/C7CP01215B (DOI)
Funder
Knut and Alice Wallenberg Foundation, KAW-2013.0020Carl Tryggers foundation , CTS 15:266
Note

QC 20160516

Available from: 2016-05-16 Created: 2016-05-16 Last updated: 2017-04-06Bibliographically approved

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