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Coupled electron-nuclear dynamics in resonant 1 sigma -> 2 pi x-ray Raman scattering of CO molecules
KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Universidade Federal Goiás, Brasilia.ORCID iD: 0000-0003-4020-0923
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2016 (English)In: Physical Review A, ISSN 2469-9926, Vol. 93, no 3, 032510Article in journal (Refereed) PublishedText
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. Vol. 93, no 3, 032510
Keyword [en]
Spectra, Excitation, Photoemission, Emission, Model
National Category
Other Physics Topics
Identifiers
URN: urn:nbn:se:kth:diva-185360DOI: 10.1103/PhysRevA.93.032510ISI: 000372399100006ScopusID: 2-s2.0-84961724217OAI: oai:DiVA.org:kth-185360DiVA: diva2:921531
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
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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