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Non-Adiabatic effects in Resonant Inelastic x-ray Scattering
Institut für Experimentalphysik, Universität Hamburg.
KTH, School of Biotechnology (BIO), Theoretical Chemistry.
KTH, School of Biotechnology (BIO), Theoretical Chemistry.
Institut für Experimentalphysik, Universität Hamburg.
Show others and affiliations
2005 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 95, no 16, 163002- p.Article in journal (Refereed) Published
Abstract [en]

We have studied the spectral features of resonant inelastic x-ray scattering of condensed ethylene with vibrational selectivity both experimentally and theoretically. Purely vibrational spectral loss features and coupled electronic and vibrational losses are observed. The one-step theory for resonant soft x-ray scattering is applied, taking multiple vibrational modes and vibronic coupling into account. Our investigation of ethylene underlines that the assignment of spectral features observed in resonant inelastic x-ray scattering of polyatomic systems requires an explicit description of the coupled electronic and vibrational loss features.

Place, publisher, year, edition, pages
2005. Vol. 95, no 16, 163002- p.
Keyword [en]
Nonadiabatic effects; Resonant inelastic X-ray scattering; Vibrational spectral loss; Energy dissipation; Ethylene; Resonance
National Category
Biochemistry and Molecular Biology
Identifiers
URN: urn:nbn:se:kth:diva-6998DOI: 10.1103/PhysRevLett.95.163002ISI: 000232558400019Scopus ID: 2-s2.0-28844452203OAI: oai:DiVA.org:kth-6998DiVA: diva2:11869
Note
QC 20100813Available from: 2007-04-20 Created: 2007-04-20 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Electron-nuclear Dynamics in Nonlinear Optics and X-ray spectroscopy
Open this publication in new window or tab >>Electron-nuclear Dynamics in Nonlinear Optics and X-ray spectroscopy
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This thesis is devoted to theoretical studies of the role of nuclear vibrations on nonlinear and linear absorption, pulse propagation, and resonant scattering of light. The molecular parameters needed for the simulations are obtained through suitable quantum chemical calculations, which are compared with available experimental data.

The first part of the thesis addresses to modeling of ampli ed spontaneous emission (ASE) in organic chromophores recently studied in a series of experiments. To explain the threshold behavior of the ASE spectra we invoke the idea of competition between di erent ASE channels and non-radiative quenching of the lasing levels. We show that the ASE spectrum changes drastically when the pump intensity approaches the threshold level, namely, when the ASE rate approaches the rate of vibrational relaxation or the rate of solute-solvent relaxation in the rst excited state. According to our simulations the ASE intensity experiences oscillations. Temporal self-pulsations of forward and backward propagating ASE pulses occur due to two reasons: i) the interaction of co- and counter-propagating ASE, and ii) the competition between the ampli ed spontaneous emission and o -resonant absorption.

In the second part of the thesis we explore two-photon absorption taking into account nuclear vibrational degrees of freedom. The theory, applied to the N101 molecule [p-nitro-p'- diphenylamine stilbene], shows that two-step absorption is red shifted relative to one-photon absorption spectrum in agreement with the measurements. The reason for this e ect is the one-photon absorption from the first excited state. Simulations show that two mechanisms are responsible for the population of this state, two-photon absorption and offresonant one-photon absorption by the wing of the spectral line.

In the third part of the thesis we study multi-photon dynamics of photobleaching by a periodical sequence of short laser pulses. It is found that the photobleaching as well as the uorescence follow double-exponential dynamics.

The fourth part of the thesis is devoted to the role of the nuclear dynamics in x-ray spectroscopy. Our studies show that the vibronic coupling of close lying core excited states strongly a ects the resonant x-ray Raman scattering from ethylene and benzene molecules. We demonstrate that the manifestation of the non-adiabatic e ects depends strongly on the detuning of photon energy from the top of photoabsorption. The electronic selection rules are shown to break down when the excitation energy is tuned in resonance with the symmetry breaking vibrational modes. Selection rules are then restored for large detuning. We obtained good agreement with experiment. Finally, our multi-mode theory is applied to simulations of the resonant Auger and x-ray absorption spectra of the ethyne molecule.

Place, publisher, year, edition, pages
Stockholm: KTH, 2007. iv, 70 p.
National Category
Medical Biotechnology (with a focus on Cell Biology (including Stem Cell Biology), Molecular Biology, Microbiology, Biochemistry or Biopharmacy)
Identifiers
urn:nbn:se:kth:diva-4339 (URN)978-91-7178-634-0 (ISBN)
Public defence
2007-05-04, FB 42, AlbaNova, Roslagstullsbacken, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100813Available from: 2007-04-20 Created: 2007-04-20 Last updated: 2010-08-13Bibliographically approved
2. Nuclear Dynamics in X-ray Absorption and Raman Scattering
Open this publication in new window or tab >>Nuclear Dynamics in X-ray Absorption and Raman Scattering
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This thesis presents theoretical studies of several x-ray spectroscopies - x-ray absorption, x-ray photoelectron emission, radiative and non-radiative resonant Raman scattering spectroscopy. The main focus point is investigating the influence of nuclear dynamics on these spectra for a variety of small molecules - naphthalene, biphenyl, ethylene, the water dimer, HCl, CO. The theoretical tools used consist of the basic equations of the relevant x-ray spectroscopy. Wave packet methods are also used. The molecular parameters needed for our simulations are obtained through suitable quantum chemical calculations, based on either wave function or density functional methods. Our simulations are compared to experimental data, where available.

Simulations of x-ray absorption and x-ray photoionization spectra for naphthalene and biphenyl show that the spectral shapes are heavily influenced by the joint effect of two factors -- chemical shifts and excitations of vibrational progression. Comparison between the two molecules and also comparison to a reference case -- benzene, provides useful insight into the molecular behavior under core excitation.

In a further step, we consider the O1s x-ray photoelectron spectrum of the water dimer. A substantial broadening of the two bands originating from the donor and the acceptor oxygen is found. It is caused by excitations of soft intermolecular vibrational modes, associated with the hydrogen bond.

Another strong influence of the nuclear dynamics is clearly seen in the resonant x-ray Raman scattering of HCl. Vibrational collapse is observed experimentally and confirmed theoretically for distinctive situations. This effect allows to eliminate completely the vibrational broadening, and hence, considerably increase the spectral resolution.

We considered also the vibrational dynamics in resonant soft x-ray Raman scattering from ethylene. The importance of vibronic coupling and symmetry effects is discussed and emphasized. We obtained excellent agreement with the experimental data.

We predict an interference effect in the resonant Auger scattering from fixed-in-space molecules. By exciting a molecule to a dissociative state and measuring the angular distribution of the Auger electrons in coincidence with the molecular ion, one can observe this effect. The interference pattern can be used after Fourier transformation for extracting structural data about the studied system.

We have found that two-center interference leads to an enhancement of the recoil effect.

Finally, it is shown that core excitation to doubly-excited dissociative Pi state is accompanied by Doppler splitting of the atomic peak in resonant Auger scattering from carbon monoxide.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. viii, 57 p.
Series
Theses in philosophy from the Royal Institute of Technology, ISSN 1650-8831
Keyword
x-ray scattering, theory, simulations, recoil, Doppler effect, nuclear dynamics, Auger, XPS
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-3902 (URN)91-7178-276-1 (ISBN)
Public defence
2006-04-21, FA 32, AlbaNova, Roslagstullsbacken 21, 09:00
Opponent
Supervisors
Note
QC 20100910Available from: 2006-04-05 Created: 2006-04-05 Last updated: 2010-09-10Bibliographically approved

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