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Femtosecond nuclear motion of HCl probed by resonant x-ray Raman scattering in the Cl 1s region
Show others and affiliations
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.

Place, publisher, year, edition, pages
2006. Vol. 73, no 2, 020706(R)- p.
Keyword [en]
fast dissociation, decay, spectroscopy, molecules, excitation, dynamics, states
National Category
Theoretical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-5554DOI: 10.1103/PhysRevA.73.020706ISI: 000235668100009Scopus ID: 2-s2.0-33644520618OAI: oai:DiVA.org:kth-5554DiVA: diva2:9955
Note
QC 20100910Available from: 2006-04-05 Created: 2006-04-05 Last updated: 2017-11-21Bibliographically approved
In thesis
1. 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
2. Theoretical studies of X-ray induced nuclear dynamics
Open this publication in new window or tab >>Theoretical studies of X-ray induced nuclear dynamics
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
Theoretical physics, Teoretisk fysik
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-296 (URN)91-7178-028-9 (ISBN)
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

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Ågren, Hans

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