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Quantum nuclear dynamics in  x-ray scattering and lasing
KTH, School of Biotechnology (BIO), Theoretical Chemistry.
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This thesis presents a theoretical study of the role of nuclear degrees of freedom in the x-ray absorption, x-ray resonant scattering  and some aspects of the interaction of matter with strong laser fields. Most numerical simulations are performed with a time-dependent wave-packet program that have proved its robustness  in previous investigations. The relevant experimental results are also presented for comparison when available.

The first problem considered in the thesis is the possibility of obtaining x-ray absorption spectra with resolution beyond the natural lifetime broadening of the core-excited electronic states. It is shown that the method of measuring x-ray absorptionin the resonant scattering mode suggested earlier for that purpose exhibits severe limitations originating from the lifetime vibrational interference between the intermediate core-excited vibrational levels. However, a broad class of molecules is found for which spectra with super-high resolution can indeed be obtained. These molecules have parallel potential energy surfaces of the core-excited and final states for the x-ray scattering process.

The interpretations of two interesting cases of x-ray absorption and Auger scattering follow. The first one is related to scattering through a doubly excited Π state in the CO molecule. A Doppler split feature near 299.4 eV and strong scattering anisotropy are  observed. Both features are well explained and reproduced by the theory. Next, theelectron-vibrational fine structure of the $O1s\rightarrow\sigma^{*}$ excitation for O2 is investigated by means of different models. We are able to single out the electronic states and interpotential crossing points responsible for the peculiar absorption profile. Based on these findings we explain and reproduce the x-ray Auger scattering spectra through the same excitation. Here we encounter a rather unusual situation in which the Auger spectra are affected by three types of the interference: Apart from the lifetime vibrational interference, a strong interference between two intermediate electronic states and an interference with the direct-scattering amplitude is also present.

The process of intramolecular vibrational redistribution (IVR) is investigated in the context of formation of amplified spontaneous emissions (ASE) inside laser-pumped gain media. IVR raises to a higher energy region the threshold pump intensity after which blue-shifted ASE is observed.

Finally, we suggest a new scheme of x-ray pump-probe spectroscopy based on the core-hole hopping in N2 induced by an infrared laser field. We investigate the result from the core-hole hoping on the vibrational structure of the x-ray absorption profile. Furthermore, by populating core-excited states with opposite parities, the laser field opens up symmetry forbidden resonant inelastic scattering channels, which can give new insights about the electronic structure of matter.

Place, publisher, year, edition, pages
Stockholm: KTH , 2008. , x, 63 p.
Series
Trita-BIO-Report, ISSN 1654-2312 ; 2008:28
National Category
Theoretical Chemistry
Identifiers
ISBN: 978-91-7415-159-6OAI: oai:DiVA.org:kth-9728DiVA: diva2:127279
Public defence
2008-12-17, FB42, AlbaNova, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Note
QC 20100917Available from: 2008-12-10 Created: 2008-12-03 Last updated: 2010-09-17Bibliographically approved
List of papers
1. X-ray absorption measured in the resonant Auger scattering mode
Open this publication in new window or tab >>X-ray absorption measured in the resonant Auger scattering mode
2008 (English)In: Physical Review Letters, ISSN 0031-9007, Vol. 101, no 7Article in journal (Refereed) Published
Abstract [en]

We report both experimental and theoretical studies on x-ray absorption measured in the resonant Auger scattering mode of gas phase carbon monoxide near the O1s -> 2 pi region. Both experiment and theory display a crucial difference between the x-ray absorption profiles obtained in the conventional and resonant scattering modes. Lifetime vibrational interference is the main source of the difference. It is demonstrated that such interference, which arises from a coherent excitation to overlapping intermediate levels, ruins the idea for obtaining x-ray absorption spectra in a lifetime broadening free regime.

Keyword
spectra, raman, excitation, molecules
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-17764 (URN)10.1103/PhysRevLett.101.073001 (DOI)000258473800017 ()2-s2.0-49549089056 (ScopusID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2010-09-16Bibliographically approved
2. X-ray absorption spectroscopy measured in resonant X-ray scattering mode: How unnatural is the resolution beyond the natural width?
Open this publication in new window or tab >>X-ray absorption spectroscopy measured in resonant X-ray scattering mode: How unnatural is the resolution beyond the natural width?
2008 (English)In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 465, no 1-3, 153-156 p.Article in journal (Refereed) Published
Abstract [en]

The aim of this work is to give a clarifying view of the ‘super-high resolution’ scheme employing X-ray absorption spectroscopy in the resonant scattering mode. If the idea is not applied carefully, unrealistic results, as ‘perfect’ resolution, can be produced. The background of the problem is that the technique of extracting lifetime-broadening-free spectra assumes a known location of the resonance in the two-dimensional map of X-ray scattering spectra. The accuracy of the latter is, however, related to the lifetime broadening of the core-excited state. Thus, a compromise must be found between the uncertainty in the position of the X-ray absorption peak and the width of the desired absorption profile.

Keyword
Absorption, Clarification, Electromagnetic wave absorption, Energy absorption, Scattering, X ray absorption, X ray absorption spectroscopy, X ray scattering, X ray spectroscopy, X rays, Absorption peaks, High-resolution, Lifetime broadening, Resonant scatterings
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-9731 (URN)10.1016/j.cplett.2008.09.067 (DOI)000260259100031 ()2-s2.0-54049113741 (ScopusID)
Note
QC 20100916Available from: 2008-12-04 Created: 2008-12-04 Last updated: 2010-09-16Bibliographically approved
3. Limitations of X-ray absorption spectroscopy of super-high resolution measured in resonant Auger mode
Open this publication in new window or tab >>Limitations of X-ray absorption spectroscopy of super-high resolution measured in resonant Auger mode
(English)Article in journal (Other academic) Submitted
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-9732 (URN)
Note
QS 20120328Available from: 2008-12-04 Created: 2008-12-04 Last updated: 2012-03-28Bibliographically approved
4. Electronic Doppler effect in resonant Auger decay of CO molecules upon excitation near a shake-up Pi resonance
Open this publication in new window or tab >>Electronic Doppler effect in resonant Auger decay of CO molecules upon excitation near a shake-up Pi resonance
2007 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 76, no 062704Article in journal (Refereed) Published
Abstract [en]

Wepresent an experimental observation of the electronic Doppler effect inresonant Auger spectra upon core excitation slightly above the carbonK edge of the CO molecule. Thus the electronic Dopplereffect has been identified in above-threshold excitation, and in atransition of symmetry. Ab initio calculations of the potentialenergy curves of the relevant states of CO and thewave packet technique have been employed to provide a theoreticalbackground to the experimental studies. The weak feature around 299.4  eVin the photoabsorption spectrum, whose decay has been investigated bythe present experiment, is assigned to double (core-valence) excitations toC 1s shake-up states |1s1−1*2 with a strong dissociative character,and the Doppler splitting of the atomic peak has beenreproduced by the simulation.

APS, 2007
Keyword
ray raman-scattering, photochemistry beamline bl27su, excited-states, shell, photoemission, radiation, dynamics, autoionization, dissociation, spectroscopy
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-9733 (URN)10.1103/PhysRevA.76.062704 (DOI)000251985900062 ()2-s2.0-37249052816 (ScopusID)
Note

Uppdaterad från manuskript till artikel: 20100910 QC 20100910

Available from: 2008-12-04 Created: 2008-12-04 Last updated: 2016-05-18Bibliographically approved
5. X-ray absorption and resonant Auger spectroscopy of O(2) in the vicinity of the O 1s ->sigma* resonance: Experiment and theory
Open this publication in new window or tab >>X-ray absorption and resonant Auger spectroscopy of O(2) in the vicinity of the O 1s ->sigma* resonance: Experiment and theory
2008 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 128, no 6, 064304Article in journal (Refereed) Published
Abstract [en]

We report on an experimental and theoretical investigation of x-ray absorption and resonant Auger electron spectra of gas phase O(2) recorded in the vicinity of the O 1s ->sigma* excitation region. Our investigation shows that core excitation takes place in a region with multiple crossings of potential energy curves of the excited states. We find a complete breakdown of the diabatic picture for this part of the x-ray absorption spectrum, which allows us to assign an hitherto unexplained fine structure in this spectral region. The experimental Auger data reveal an extended vibrational progression, for the outermost singly ionized X (2)Pi(g) final state, which exhibits strong changes in spectral shape within a short range of photon energy detuning (0 eV>Omega>-0.7 eV). To explain the experimental resonant Auger electron spectra, we use a mixed adiabatic/diabatic picture selecting crossing points according to the strength of the electronic coupling. Reasonable agreement is found between experiment and theory even though the nonadiabatic couplings are neglected. The resonant Auger electron scattering, which is essentially due to decay from dissociative core-excited states, is accompanied by strong lifetime-vibrational and intermediate electronic state interferences as well as an interference with the direct photoionization channel. The overall agreement between the experimental Auger spectra and the calculated spectra supports the mixed diabatic/adiabatic picture.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2008
Keyword
Auger electron spectroscopy, Electron scattering, Electronic states, Excited states, Potential energy, Vibrational spectra, X ray absorption, Resonant Auger spectroscopy, Spectral region, Vicinity
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-9734 (URN)10.1063/1.2831920 (DOI)000253238200017 ()18282035 (PubMedID)2-s2.0-39349091895 (ScopusID)
Note

QC 20100916

Available from: 2008-12-04 Created: 2008-12-04 Last updated: 2016-07-22Bibliographically approved
6. Pseudo-resonance formation in X-ray absorption spectrum of oxygen molecule
Open this publication in new window or tab >>Pseudo-resonance formation in X-ray absorption spectrum of oxygen molecule
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-9735 (URN)
Note
QC 20100916Available from: 2008-12-04 Created: 2008-12-04 Last updated: 2010-09-16Bibliographically approved
7. Role of intramolecular vibrational redistribution on dynamics of cavityless lasing
Open this publication in new window or tab >>Role of intramolecular vibrational redistribution on dynamics of cavityless lasing
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-9736 (URN)
Note
QC 20100916Available from: 2008-12-04 Created: 2008-12-04 Last updated: 2010-09-16Bibliographically approved
8. X-ray absorption of N2 accompanied by infrared-induced transitions between the ungerade and gerade core levels
Open this publication in new window or tab >>X-ray absorption of N2 accompanied by infrared-induced transitions between the ungerade and gerade core levels
2008 (English)In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 41, no 14, 145601- p.Article in journal (Refereed) Published
Abstract [en]

We study a two-colour pump–probe scheme of x-ray absorption accompanied by core-hole hopping in the field of a strong IR laser. The process is exemplified for fixed-in-space and randomly oriented homonuclear diatomic molecules N2 near the 1σu → 1πg x-ray absorption transition. The laser field mixes the core holes of opposite parities and causes Rabi splitting of the core-excited states. The IR field results in spectral broadening and shifts of the x-ray resonances as well as decrease of x-ray photoabsorption. The Stark broadening of the x-ray absorption spectrum depends on the orientation of the molecule and the angle between the polarization vectors of the x-ray and IR fields. The spectral changes caused by the IR field are weaker for randomly oriented molecules in comparison with fixed-in-space molecules.

Keyword
Absorption, Electromagnetic wave absorption, Pulsed laser deposition, Pumping (laser), Space probes, X ray absorption, Homonuclear diatomic molecules, IR lasers, Pump probe scheme, X ray absorption (XAS)
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-9737 (URN)10.1088/0953-4075/41/14/145601 (DOI)000257370200021 ()2-s2.0-47249087705 (ScopusID)
Note

QC 20100916

Available from: 2008-12-04 Created: 2008-12-04 Last updated: 2016-04-20Bibliographically approved
9. Resonant inelastic X-ray Raman scattering induced by Rabi flopping of core holes
Open this publication in new window or tab >>Resonant inelastic X-ray Raman scattering induced by Rabi flopping of core holes
2008 (English)In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 453, no 1-3, 117-121 p.Article in journal (Refereed) Published
Abstract [en]

A new scheme of X-ray pump-probe experiment is suggested in this Letter, namely resonant inelastic X-ray scattering accompanied by core-hole hopping induced by a strong laser field. In particular, we study the dynamics of X-ray Raman scattering of N-2 molecules in a strong IR field. The laser-induced mixing of the core holes of opposite parities opens symmetry forbidden scattering channels. The strength of the symmetry forbidden channels strongly depends on the interrelationship between the time of Rabi flopping of the core holes and the scattering duration or the duration of the X-ray pulse.

Keyword
Inelastic scattering, Laser radiation, X ray analysis, Core holes, Rabi flopping
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-9739 (URN)10.1016/j.cplett.2008.01.023 (DOI)000253883500023 ()2-s2.0-39149085660 (ScopusID)
Note
QC 20100917Available from: 2008-12-04 Created: 2008-12-04 Last updated: 2010-09-17Bibliographically approved

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