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Resonant elastic X-ray scattering in H2O, D2O and HDO with vibrational resolution: mode filtering, mode localization, and potential energy surface mapping
KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. (Theoretical chemistry and biology)
KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. (Theoretical Chemistry and Biology)ORCID iD: 0000-0003-4020-0923
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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: urn:nbn:se:kth:diva-187012OAI: oai:DiVA.org:kth-187012DiVA: diva2:928542
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
In thesis
1. Coupled electron-nuclear dynamics in inelastic X-ray scattering
Open this publication in new window or tab >>Coupled electron-nuclear dynamics in inelastic X-ray scattering
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
X-ray spectroscopy, resonant inelastic X-ray scattering, water, carbon monoxide
National Category
Theoretical Chemistry
Research subject
Theoretical Chemistry and Biology
Identifiers
urn:nbn:se:kth:diva-186530 (URN)978-91-7595-988-7 (ISBN)
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

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