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Resonant inelastic X-ray scattering and X-ray absorption of methanol at the near oxygen K-edge
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology. KTH.
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

We report on a theoretical analysis of core-excitation spectra of gas and liquid phase methanol asobtained with use of X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering(RIXS). The electronic transitions are studied with complementary computational methods includ-ing strict and extended second-order algebraic diagrammatic construction (ADC(2) and ADC(2)-x),restricted active space second-order perturbation theory (RASPT2), and time-dependent densityfunctional theory (TDDFT)—providing a complete assignment of the near oxygen K-edge XAS.We show that multimode nuclear dynamics is of crucial importance for explaining the availableexperimental XAS and RIXS spectra. Multimode nuclear motions was considered in a developedmixed representation where dissociative states and highly excited vibrational modes are accuratelytreated with a time-dependent wave packet technique while the remaining active vibrational modesare described using Franck–Condon amplitudes. Particular attention is paid to the polarizationdependence of RIXS and the effects of the isotope substitution on the RIXS profile in the case ofdissociative core-excited states. Our approach predicts the splitting of the 2a RIXS peak to bedue to an interplay between molecular and atomic-like features arising in the course of transitionsbetween dissociative core- and valence-excited states. The dynamical nature of the splitting of the2a peak in RIXS of liquid methanol near pre-edge core excitation is shown. The theoretical resultsare in good agreement with available experimental data.

National Category
Atom and Molecular Physics and Optics Theoretical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-227941OAI: oai:DiVA.org:kth-227941DiVA, id: diva2:1205766
Note

QC 20180515

Available from: 2018-05-15 Created: 2018-05-15 Last updated: 2018-05-15Bibliographically approved
In thesis
1. Quantum Nuclear Dynamics in Resonant X-ray Scattering of Gas-Phase and Liquid Systems
Open this publication in new window or tab >>Quantum Nuclear Dynamics in Resonant X-ray Scattering of Gas-Phase and Liquid Systems
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis focuses on the role of the nuclear degrees of freedom in X-ray induced molecular processes. An important part of it is devoted to establishing theoretical principles to model and interpret high-resolution resonant X-ray scattering experiments in gases and liquids. Our investigations address the resonant inelastic x-ray scattering (RIXS) of H2O(g), H2O(l) and CH3OH(g) and Auger emission induced by hard X-rays in CO(g). The simulations for gas-phase systems are based on a multi-mode wave packet formalism and on potential energy surfaces computed with multi-configurational approaches.

For liquid systems, we propose a classical/quantum formalism for simulating RIXS based on a combination of ab initio molecular dynamics, density functional theory calculations and quantum nuclear wave packet propagation. The developed model is able to reproduce the experimental observation of shortening of the vibrational progression in H2O(l).

We show that electronically-elastic RIXS has an intrinsic capability to map the potential energy surface and to carry out vibrational analysis of the electronic ground state in free molecules as well as liquids. For gas-phase water, we see that the landscape of different core-excited states cause the nuclear wave packet to be localized along specific directions thus allowing to reconstruct one-dimensional potential energy curves. For liquid water, we propose a model for deriving, from experiment, confidence intervals for the molecular potential energy curves along the OH bonds, which are determined by the local arrangement of the hydrogen bond network.

We also investigate the role of ultra-fast rotations induced by photoionization by hard X-rays. In this case, the ejection of a fast photoelectron results in an ultra-fast rotational motion of the molecule, which combined with the anisotropy of the Auger process causes the spectral profile to be split due to a dynamical Doppler effect.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2018. p. 88
Series
TRITA-CBH-FOU ; 2018:24
Keywords
resonant inelastic X-ray scattering, X-ray absorption, water, methanol, CO, rotational doppler effect, recoil, wave packet, non-Franck-Condon effect, ultra-fast molecular dissociation, potential energy surface, hydrogen bond, liquid
National Category
Theoretical Chemistry Physical Sciences Atom and Molecular Physics and Optics
Research subject
Theoretical Chemistry and Biology
Identifiers
urn:nbn:se:kth:diva-227962 (URN)978-91-7729-806-9 (ISBN)
Public defence
2018-06-12, FA32, AlbaNova University Center, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20180515

Available from: 2018-05-15 Created: 2018-05-15 Last updated: 2018-05-16Bibliographically approved
2. Multimode resonant X-ray scattering of free molecules
Open this publication in new window or tab >>Multimode resonant X-ray scattering of free molecules
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is focused on the role that nuclear dynamics plays in the formation of X-ray absorption (XAS) and resonant inelastic X-ray scattering (RIXS) spectra of multimode free molecules. A combined approach based on ab initio electronic structure methods and quantum nuclear wave packet dynamics is applied to two systems -- water and methanol in the gas phase. An IR-pump – X-ray-probe spectroscopy of vibrationally excited water and its isotope substitutions is employed to explore different vibrational progressions of the final electronic state due to a spatial filtration of the vibrations in the core-excited state and selection rules. It was demonstrated the possibility to use RIXS as a tool to study X-ray absorption from a selected vibrational level of the ground state. IR-pump – X-ray-probe spectroscopy applied to the HDO molecule sheds light on the old classical problem of wave function collapse: we demonstrate numerically the gradual collapse of the initially localised vibrational wave function in the HDO molecule. It is also explained the dynamical nature of the splitting of the 1b1 peak in the RIXS spectrum of H2O, HDO and D2O molecules. This splitting is referred to close-lying molecular and atomic-like peaks. In order to study the methanol molecule a special theoretical tool for studies of multimode molecules has been developed. This approach combines the advantages of the quantum wave packet technique for simulations of the dynamics in dissociative states with the efficiency of the Franck-Condon method for computing transitions between bound states. It is shown that the multimode nuclear dynamics plays an important role in XAS and RIXS spectra of methanol. The XAS and RIXS spectra formation was explained taking into account different dynamics in different core-excited potential energy surfaces, as well as the entanglement of vibrational modes by anharmonicity and by the life-time vibrational interference.

Place, publisher, year, edition, pages
Stockholm, Sweden: KTH Royal Institute of Technology, 2018. p. 73
Series
TRITA-CBH-FOU ; 2018:23
Keywords
X-ray absorption spectroscopy, core-excited state, nuclear dynamic, wave-packet, resonant inelastic X-ray scattering, Franck-Condon, water, methanol, water isotopomer, pump-probe, quantum chemistry, ultrafast dissociation
National Category
Atom and Molecular Physics and Optics
Research subject
Chemistry; Physics
Identifiers
urn:nbn:se:kth:diva-227971 (URN)978-91-7729-800-7 (ISBN)
Public defence
2018-06-11, FA32, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20180516

Available from: 2018-05-16 Created: 2018-05-15 Last updated: 2018-05-16Bibliographically approved

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