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Soft X-ray Scattering Dynamics Close to Core Ionization Thresholds in Atoms and Molecules
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this Thesis studies of highly excited states in gas-phase atoms and molecules (He, Ne, N2, O2, N2O and CO2) using a variety of synchrotron-radiation based techniques are presented. The three techniques used most frequently are X-ray-emission-threshold-electron coincidence (XETECO), X-ray emission spectroscopy (XES) and X-ray photoelectron spectroscopy (XPS) and they are all given a brief introduction.

The fluorescence yield (FY) from doubly excited states in helium near the N=2 threshold(s) has been investigated in weak static external magnetic and electric fields, but also in a field free environment. The FY spectra in weak static magnetic fields show the importance of including the diamagnetic interaction in the theoretical models. The presence of weak static electric fields shows that even weak fields (as low as 44 V/cm) has a great impact on the observed FY spectra. Resonant XES spectra from some of the first doubly excited states in helium has been recorded in a field free environment, and compared to theory.

The XETECO technique is presented and the first XETECO results from Ne, N2, O2, CO2 and N2O are shown, together with interpretations of possible threshold dynamics. I show that XETECO can be interpreted as threshold photoelectron spectra free from post collision interaction, and can hence be compared to above threshold XPS measurements. The observed below-threshold structures in the XETECO spectra are discussed and given a tentative explanation. The results from the analysis of the N2O XETECO spectrum lead to further investigations using XPS. Results showing the vibrational parameters and vibrationally resolved cross-sections and asymmetry parameters for N2O are presented together with theoretical predictions.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2007. , p. 106
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 297
Keywords [en]
Physics, Soft X-ray emission, Resonant inelastic X-ray scattering, Double excitations, Helium, X-ray-emission-threshold-electron coincidence
Keywords [sv]
Fysik
Identifiers
URN: urn:nbn:se:uu:diva-7832ISBN: 978-91-554-6874-3 (print)OAI: oai:DiVA.org:uu-7832DiVA, id: diva2:170153
Public defence
2007-05-16, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15
Opponent
Supervisors
Available from: 2007-04-24 Created: 2007-04-24 Last updated: 2011-01-24Bibliographically approved
List of papers
1. X-ray-emission-threshold-electron coincidence spectroscopy
Open this publication in new window or tab >>X-ray-emission-threshold-electron coincidence spectroscopy
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2004 In: Journal of Electron Spectroscopy and Related Phenomena, Vol. 141, no 2-3, p. 161-170Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-95801 (URN)
Available from: 2007-04-24 Created: 2007-04-24Bibliographically approved
2. Core level ionization dynamics in small molecules studied by x-ray-emission threshold-electron coincidence spectroscopy
Open this publication in new window or tab >>Core level ionization dynamics in small molecules studied by x-ray-emission threshold-electron coincidence spectroscopy
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2005 In: Physical Review A, ISSN 1050-2947, Vol. 71, p. 012506-Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-95802 (URN)
Available from: 2007-04-24 Created: 2007-04-24 Last updated: 2016-04-26Bibliographically approved
3. Oxygen K Edge X-ray-Emission-Threshold-Electron Coincidence Spectrum of CO2
Open this publication in new window or tab >>Oxygen K Edge X-ray-Emission-Threshold-Electron Coincidence Spectrum of CO2
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2007 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 76, no 2, p. 022505-Article in journal (Refereed) Published
Abstract [en]

The oxygen K -edge x-ray-emission-threshold-electron coincidence spectrum of CO2 is presented. A two-step model, describing the result as a threshold-photoelectron spectrum free from post-collision interaction effects, predicts the salient features of the measured spectrum. Small discrepancies from the predictions are discussed in terms of threshold ionization dynamics.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-95803 (URN)10.1103/PhysRevA.76.022505 (DOI)000249154900061 ()
Available from: 2007-04-24 Created: 2007-04-24 Last updated: 2017-12-14
4. Resonant Inelastic Photon Scattering in Helium
Open this publication in new window or tab >>Resonant Inelastic Photon Scattering in Helium
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In: In manuscriptArticle in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-95804 (URN)
Available from: 2007-04-24 Created: 2007-04-24Bibliographically approved
5. Double Excitations of Helium in Weak Static Electric Fields
Open this publication in new window or tab >>Double Excitations of Helium in Weak Static Electric Fields
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2006 In: Physical Review Letters, ISSN 0031-9007, Vol. 96, p. 043002-Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-95805 (URN)
Available from: 2007-04-24 Created: 2007-04-24 Last updated: 2016-04-26Bibliographically approved
6. Magnetic-field induced enhancement in the fluorescence yield spectrum of doubly excited states in helium
Open this publication in new window or tab >>Magnetic-field induced enhancement in the fluorescence yield spectrum of doubly excited states in helium
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2006 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 97, no 25, p. 253002-Article in journal (Refereed) Published
Abstract [en]

An influence of static magnetic fields on the fluorescence yield spectrum of He in the vicinity of the N=2 thresholds has been observed. The experimental results are in excellent agreement with predictions based on multichannel quantum defect theory, and it is demonstrated that the Rydberg electron ℓ mixing due to the diamagnetic interaction is essential for the description of the observed fluorescence yield intensity enhancement.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-95806 (URN)10.1103/PhysRevLett.97.253002 (DOI)000243414600018 ()
Available from: 2007-04-24 Created: 2007-04-24 Last updated: 2017-12-14
7. Vibrationally resolved nitrogen K-shell photoelectron spectra of the dinitrogen oxide molecule: Experiment and theory
Open this publication in new window or tab >>Vibrationally resolved nitrogen K-shell photoelectron spectra of the dinitrogen oxide molecule: Experiment and theory
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2007 (English)In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 438, no 1-3, p. 14-19Article in journal (Refereed) Published
Abstract [en]

Vibrationally resolved Nc and Nt K-shell photoelectron spectra of the dinitrogen oxide have been studied experimentally and theoretically. Vibrational frequencies for the Nc and Nt 1s ionized states obtained from the 2D potential surfaces computed by the CCSD(T) method within the equivalent core approximation reasonably agree with the experimental values. Experimental relative intensities of the vibrational structure are reasonably reproduced by the multi-channel Schwinger configuration interaction method (MCSCI) with the computed 2D potential surfaces. Improved relaxed geometries of these core–hole states are obtained from fitting the experimental spectra using the MCSCI calculations and regarding the bond lengths as fitting parameters.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-95807 (URN)10.1016/j.cplett.2007.02.057 (DOI)000245776300003 ()
Available from: 2007-04-24 Created: 2007-04-24 Last updated: 2017-12-14Bibliographically approved
8. Vibrationally resolved partial cross sections and asymmetry parameters for nitrogen K-shell photoionization of the N2O molecule
Open this publication in new window or tab >>Vibrationally resolved partial cross sections and asymmetry parameters for nitrogen K-shell photoionization of the N2O molecule
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2007 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 76, no 1, p. 012506-Article in journal (Refereed) Published
Abstract [en]

We have measured the vibrationally resolved partial cross sections σ(v1,v2,v3) and asymmetry parameters β(v1,v2,v3) for Nc and Nt K-shell photoionization of the N2O molecule in the σ* shape resonance region above the Nt and Nc K-shell ionization thresholds. Nc K-shell photoionization of the N2O molecule predominantly causes the excitation of the quasisymmetric vibrations (v1), whereas Nt K-shell photoionization causes both quasisymmetric and quasiantisymmetric vibrations (v1 and v3) to be excited. The shape resonance energy in the Nc K-shell photoionization increases with an increase in v1. The β(v1,0,0) curves for the Nc K-shell photoionization exhibit maxima at energies close to the shape resonance energies for the individual values of v1. The shape resonance energy in the Nt K-shell photoionization decreases with an increase in v1 and slightly increases with an increase in v3. The β(v1,0,0) curves show a significant state dependence in the region of the shape resonance, with the curves shifting to lower energy as v1 increases. The vibrational state dependence of the cross sections σ(v1,v2,v3) and asymmetry parameters β(v1,v2,v3) are well reproduced by the theoretical calculations using the multichannel Schwinger configuration interaction (MCSCI) method, including both the Nc and Nt ion states.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-95808 (URN)10.1103/PhysRevA.76.012506 (DOI)000248486600081 ()
Available from: 2007-04-24 Created: 2007-04-24 Last updated: 2017-12-14

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