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Theoretical studies of X-ray induced nuclear dynamics
KTH, School of Engineering Sciences (SCI), Physics.
2005 (English)Licentiate thesis, comprehensive summary (Other scientific)
Abstract [en]

The present thesis is a theoretical study of several x-ray spectroscopies { x-ray absorption, xray photoelectron, radiative and non-radiative resonant Raman scattering spectroscopy. The main focus point is investigating the role of the nuclear dynamics in molecules (naphthalene, biphenyl, the water dimer, HCl) on these spectra.

The theoretical tools we use 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, mainly based on either wave function or density functional methods. Our simulations are compared with 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 inuenced by the joint e ect of two factors { chemical shifts and excitations of vibrational progression. In both of the studied molecules, similar vibrational modes are excited, giving rise to a signi cant vibrational broadening of the spectra. Comparison between the two molecules and also comparison to the 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 inuence of the nuclear dynamics is clearly seen in the resonant x-ray Raman scattering of HCl. Vibrational collapse is observed experimentally and con rmed theoretically for two cases: resonant excitation of the K line and o -resonant excitation of the elastic peak. These two collapses can be strictly realized for excitations in the hard x-ray region. Our considerations show that using this technique, one can eliminate the broadenings caused by the lifetime of the core excited state and the vibrational broadening, and hence, considerably increase the spectral resolution.

Finally, we predict an interference e ect in the resonant Auger scattering from xed-inspace 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 e ect. The interference pattern can be used after Fourier transformation for extracting structural data about the studied system.

Place, publisher, year, edition, pages
Stockholm: KTH , 2005. , 42 p.
Keyword [en]
Theoretical physics
Keyword [sv]
Teoretisk fysik
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-296ISBN: 91-7178-028-9 (print)OAI: oai:DiVA.org:kth-296DiVA: diva2:8700
Presentation
2005-05-19, Sal FB32, AlbaNova, 14:00
Supervisors
Note
QC 20101215Available from: 2005-07-11 Created: 2005-07-11 Last updated: 2010-12-15Bibliographically approved
List of papers
1. Core-excitations of naphthalene: Vibrational structure versus chemical shifts
Open this publication in new window or tab >>Core-excitations of naphthalene: Vibrational structure versus chemical shifts
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2004 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 121, no 12, 5733-5739 p.Article in journal (Refereed) Published
Abstract [en]

The initial state chemical shifts and vibrational fine structure of core excitations of naphthalene were analyzed using high-resolution x-ray photoelectron emission (XPS) and near-edge x-ray absorption fine structure (NEXAFS) spectra. The carbon atoms at peripheral sites were found to experience a small chemical shift and exhibit similar charge-vibrational coupling. The C-H stretching modes provide significant contributions to overall shape of spectra in the XPS spectra. The results show that vibrational fine structure dominates by particular C-C stretching modes, and in XPS of C2 and C3 sites also by high-energy C-H stretching modes.

Keyword
Approximation theory, Carbon, Carrier concentration, Electron transitions, Harmonic analysis, Kinetic energy, Mathematical models, Molecular dynamics, Molecular vibrations, Photoemission, Photoionization, Relaxation processes, X ray photoelectron spectroscopy
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-5551 (URN)10.1063/1.1784450 (DOI)000223872000020 ()2-s2.0-5444257939 (Scopus ID)
Note
QC 20100906 20110916Available from: 2006-04-05 Created: 2006-04-05 Last updated: 2017-11-21Bibliographically approved
2. Core-excitations of biphenyl
Open this publication in new window or tab >>Core-excitations of biphenyl
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2005 (English)In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 109, no 7, 1330-1336 p.Article in journal (Refereed) Published
Abstract [en]

High-resolution C(1s) near-edge X-ray absorption and X-ray photoionization spectra of the free biphenyl molecule are presented and theoretically analyzed in order to allow an assignment of the observed spectral features. Finite lifetime broadening, a high density of vibrational states, and a strong overlap of contributions from chemically different carbon atom sites only partially allow resolving the vibrational fine structure. However, the shape and width of the spectral profiles are strongly determined by both chemical shifts and vibronic effects. In particular, different from photoionization of valence levels, both types of core level spectra do not contain contributions from dihedral modes which are related to the twisting motion of the two phenyl rings. Contrary to naphthalene, C-H stretching modes are significantly enhanced in the core excitation spectra of biphenyl while the contributions from C-C stretching modes are reduced.

Keyword
Absorption spectroscopy, Chemical bonds, Computer simulation, Crucibles, Differentiation (calculus), Electron energy levels, Molecular vibrations, Oligomers, Oscillators (electronic), Photoionization, Resonance, X ray photoelectron spectroscopy
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-5552 (URN)10.1021/jp045447z (DOI)000227108500010 ()2-s2.0-14644427195 (Scopus ID)
Note
QC 20100906Available from: 2006-04-05 Created: 2006-04-05 Last updated: 2017-11-21Bibliographically approved
3. A theoretical study of the role of the hydrogen bond on core ionization of the water dimer
Open this publication in new window or tab >>A theoretical study of the role of the hydrogen bond on core ionization of the water dimer
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2005 (English)In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 312, no 1-3, 311-318 p.Article in journal (Refereed) Published
Abstract [en]

Motivated by the interest in using X-ray spectra for probing of hydrogen bonded networks we developed a quantum model for simulations of the electronic-vibrational profile of the X-ray core photoelectron spectrum of the water dimer. It is found that the potential surfaces of the donor and acceptor O1s core-ionized states of this system display a qualitative difference. Large gradients of the potential in the core ionized state along some intermolecular coordinates combined with small vibrational frequencies breaks down completely the harmonic approximation. The band profiles are therefore treated using a quasi-continuum approximation. The weak hydrogen bonding and the drastic change of water dimer potential under core ionization is responsible for the anomalously strong vibrational broadening: 0.4 eV for the acceptor band and 0.6 eV for the donor band. The core ionization of the donor oxygen is accompanied by proton transfer which should be observable in X-ray fluorescence or Auger spectra.

Place, publisher, year, edition, pages
Elsevier, 2005
Keyword
X-ray photoionization, hydrogen bonding
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-5553 (URN)10.1016/j.chemphys.2004.12.006 (DOI)000228206700033 ()2-s2.0-15744404650 (Scopus ID)
Note

QC 20100825

Available from: 2006-04-05 Created: 2006-04-05 Last updated: 2017-11-21Bibliographically approved
4. Femtosecond nuclear motion of HCl probed by resonant x-ray Raman scattering in the Cl 1s region
Open this publication in new window or tab >>Femtosecond nuclear motion of HCl probed by resonant x-ray Raman scattering in the Cl 1s region
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2006 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 73, no 2, 020706(R)- p.Article in journal (Refereed) Published
Abstract [en]

Femtosecond dynamics are observed by resonant x-ray Raman scattering (RXS) after excitation along the dissociative Cl 1s -> 6 sigma(*) resonance of gas-phase HCl. The short core-hole lifetime results in a complete breakdown of the common nondispersive behavior of soft-x-ray transitions between parallel potentials. We evidence a general phenomenon of RXS in the hard-x-ray region: a complete quenching of vibrational broadening. This opens up a unique opportunity for superhigh resolution x-ray spectroscopy beyond vibrational and lifetime limitations.

Keyword
fast dissociation, decay, spectroscopy, molecules, excitation, dynamics, states
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-5554 (URN)10.1103/PhysRevA.73.020706 (DOI)000235668100009 ()2-s2.0-33644520618 (Scopus ID)
Note
QC 20100910Available from: 2006-04-05 Created: 2006-04-05 Last updated: 2017-11-21Bibliographically approved
5. Interchannel interference in resonant Auger scattering from fixed-in-space molecules as a technique for structure determination
Open this publication in new window or tab >>Interchannel interference in resonant Auger scattering from fixed-in-space molecules as a technique for structure determination
2004 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 70, no 3, 032507- p.Article in journal (Refereed) Published
Abstract [en]

A method for structure determination of polyatomic molecules with equivalent atoms is suggested. The method is based on an interference pattern in the resonant Auger scattering process. This pattern is caused by interference of resonant Auger channels corresponding to a core hole localized on different equivalent atoms. The predicted effect can be observed in angular resolved electron-ion coincidence measurements or, alternatively, using the ordinary Auger technique on surface-oriented molecules.

Keyword
ray raman-scattering, k-edge spectra, angular-distribution, high-resolution, decay, o2, dissociation, electrons, n2
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-23820 (URN)10.1103/PhysRevA.70.032507 (DOI)000224623000065 ()2-s2.0-19644400661 (Scopus ID)
Note
QC 20100525 QC 20110923Available from: 2010-08-10 Created: 2010-08-10 Last updated: 2017-12-12Bibliographically approved

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