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Quantum Nuclear Dynamics in Resonant X-ray Scattering of Gas-Phase and Liquid Systems
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.ORCID iD: 0000-0001-9696-2498
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 [en]
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
ISBN: 978-91-7729-806-9 (print)OAI: oai:DiVA.org:kth-227962DiVA, id: diva2:1205912
##### Public defence
2018-06-12, FA32, AlbaNova University Center, Roslagstullsbacken 21, Stockholm, 10:00 (English)
##### Note

QC 20180515

Available from: 2018-05-15 Created: 2018-05-15 Last updated: 2018-05-16Bibliographically approved
##### List of papers
1. 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
2017 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 30, p. 19573-19589Article 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.

##### Place, publisher, year, edition, pages
Royal Society of Chemistry, 2017
##### Keywords
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)000407053000006 ()28352891 (PubMedID)2-s2.0-85027313711 (Scopus ID)
##### Funder
Knut and Alice Wallenberg Foundation, KAW-2013.0020Carl Tryggers foundation , CTS 15:266Swedish Research Council
##### Note

QC 20160516

Available from: 2016-05-16 Created: 2016-05-16 Last updated: 2018-05-15Bibliographically approved
2. 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
2017 (English)In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 8, p. 14165-1-14165-7Article 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
##### Keywords
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: 2018-05-15Bibliographically approved
3. One-dimensional cuts through multidimensional potential energy surfaces by tunable X-rays
Open this publication in new window or tab >>One-dimensional cuts through multidimensional potential energy surfaces by tunable X-rays
##### Abstract [en]

The concept of the potential-energy surface (PES) and directional reaction coordinates is the backbone of ourdescription of chemical reaction mechanisms. Although the eigenenergies of the nuclear Hamiltonian uniquely link a PES to its spectrum, this information is in general experimentally inaccessible in large polyatomic systems. This is due to (near) degenerate rovibrational levels across the parameter space of all degrees of freedom, which effectively forms a pseudospectrum given by the centers of gravity of groups of close-lying vibrational levels. We show here that resonant inelastic x-ray scattering (RIXS) constitutes an ideal probe for revealing one-dimensional cuts through the ground-state PES of molecular systems, even far away from the equilibrium geometry, where the independent-mode picture is broken. We strictly link the center of gravity of close-lying vibrational peaks in RIXS to a pseudospectrum which is shown to coincide with the eigenvalues of an effective one-dimensional Hamiltonian along the propagation coordinate of the core-excited wave packet. This concept, combined with directional and site selectivity of the core-excited states, allows us to experimentally extract cuts through the ground-state PES along three complementary directions for the showcase H2O molecule.

##### National Category
Theoretical Chemistry Atom and Molecular Physics and Optics
##### Identifiers
urn:nbn:se:kth:diva-227948 (URN)
##### Note

QC 20180515

Available from: 2018-05-15 Created: 2018-05-15 Last updated: 2019-10-09Bibliographically approved
4. Anomalous polarization dependence in vibrationally resolved RIXS of H2O
Open this publication in new window or tab >>Anomalous polarization dependence in vibrationally resolved RIXS of H2O
##### Abstract [en]

It is well established that different electronic channels, in resonant inelastic X-ray scattering (RIXS), display different polarization dependences due to different orientations of their corresponding transition dipole moments in the molecular frame. However, this effect does not influence the vibrational progression in the Franck-Condon approximation. We have found that the transition dipole moments of core-excitation and de-excitation experience ultrafast rotation during the dissociation in intermediate core-excited state. This rotations makes the vibrational progression in RIXS spectra sensitive to the polarisation of the X-ray photons. The studied effect is exemplified for the RIXS of the water molecule through the dissociative core-excited state where the vibrational scattering anisotropy is accompanied also by violation of parity selection rules for vibrations.

##### National Category
Physical Sciences Atom and Molecular Physics and Optics Theoretical Chemistry
##### Identifiers
urn:nbn:se:kth:diva-227947 (URN)
##### Note

QC 20180515

Available from: 2018-05-15 Created: 2018-05-15 Last updated: 2018-05-15Bibliographically approved
5. Probing hydrogen bond strength in liquid water by resonant inelastic X-ray scattering
Open this publication in new window or tab >>Probing hydrogen bond strength in liquid water by resonant inelastic X-ray scattering
##### Abstract [en]

The potential energy surface is widely used powerful concept in chemical physics. However, direct experimental access to the local potential energy surface in liquid especially in systems  with strong hydrogen bonds is lacking. We develop general technique demonstrated  for liquid water how to reconstruct from state-of-the-art  sub-natural linewidth resonant inelastic X-ray scattering (RIXS)  the local distribution of OH potential energy curves,  separately for OH bonds with weak and strong hydrogen bond. By this we are able to look on the local structure by characterising  selectively the strength of the hydrogen bond. We present a detailed analysis of the formation of the vibrationally resolved RIXS of liquids using a classical/quantum formalism  based on a combination of {\it ab initio} molecular dynamics, density functional theory calculations and quantum nuclear wave packet propagation. Theory nicely explains shortening of the vibrational progression in liquid phase in comparison with RIXS of free water molecules seen in the experiment by fluctuation of the hydrogen bond  network and coherent excitation of both OH bonds.

##### National Category
Theoretical Chemistry Atom and Molecular Physics and Optics
##### Identifiers
urn:nbn:se:kth:diva-227951 (URN)
##### Note

QC 20180515

Available from: 2018-05-15 Created: 2018-05-15 Last updated: 2018-05-15Bibliographically approved
6. Resonant inelastic X-ray scattering and X-ray absorption of methanol at the near oxygen K-edge
Open this publication in new window or tab >>Resonant inelastic X-ray scattering and X-ray absorption of methanol at the near oxygen K-edge
##### 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:nbn:se:kth:diva-227941 (URN)
##### Note

QC 20180515

Available from: 2018-05-15 Created: 2018-05-15 Last updated: 2018-05-15Bibliographically approved
7. Recoil-induced ultrafast molecular rotation probed by dynamical rotational Doppler effect
Open this publication in new window or tab >>Recoil-induced ultrafast molecular rotation probed by dynamical rotational Doppler effect
##### Abstract [en]

Observing and controlling molecular motion, and in particular rotation,is a fundamental topic in physics and chemistry. In order toinitiate ultrafast rotation, one needs a way to transfer a large angularmomentum to the molecule. As a showcase, this was performedby hard x-ray C1s ionization of carbon monoxide, accompanied byspinning-up the molecule via the recoil “kick” of the emitted fast photoelectron.To visualize this molecular motion, we use the dynamicalrotational Doppler effect and an X-ray “pump-probe” device offeredby nature itself: the recoil-induced ultrafast rotation is probed by subsequentAuger electron emission. The time information in our experimentorigins from the natural delay between the C1s photoionizationinitiating the rotation and the ejection of the Auger electron. From amore general point of view, time-resolved measurements can be performedin two ways: either to vary the "delay" time as in conventionaltime-resolved pump-probe spectroscopy and to use the dynamicsgiven by the system, or to keep constant "delay" time and to manipulatethe dynamics. Since in our experiment we cannot change the delaytime given by the core-hole lifetime $\tau$, we use the second optionand control the rotational speed by changing the kinetic energy of thephotoelectron. The recoil-induced rotational dynamics controlled insuch a way is observed as a photon-energy dependent asymmetryof the Auger lineshape, in full agreement with theory. This asymmetryis explained by a significant change of the molecular orientationduring the core-hole lifetime, which is comparable with the rotationalperiod.

##### National Category
Physical Sciences Atom and Molecular Physics and Optics
##### Identifiers
urn:nbn:se:kth:diva-227960 (URN)
##### Note

QC 20180515

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

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Cite
Citation style
• apa
• ieee
• modern-language-association-8th-edition
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