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Recoil-induced ultrafast molecular rotation probed by dynamical rotational Doppler effect
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.ORCID iD: 0000-0002-1763-9383
##### 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
OAI: oai:DiVA.org:kth-227960DiVA, id: diva2:1205846
##### 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)
##### Note

QC 20180515

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

#### Open Access in DiVA

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Ågren, Hans

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