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Detailed Theoretical and Experimental Description of Normal Auger Decay in O2
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Surface and Interface Science.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Surface and Interface Science.
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2008 (English)In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, Vol. 41, no 12, 125101- p.Article in journal (Refereed) Published
Abstract [en]

The normal Auger electron spectrum of the O-2 molecule is assigned in detail on the basis of ab initio valence configuration interaction (CI) wavefunctions. Potential energy curves of the ground state, the core-ionized states and the doubly charged final states are calculated and Auger decay rates are obtained with the one-centre approximation. Using the lifetime vibrational interference method, band shapes are obtained for all contributions to the Auger spectrum. The calculated Auger electron spectrum allows us to identify all features observed experimentally. Significant differences to previous assignments are reported. A quantitative simulation of the spectrum is given on the basis of a curve-fitting procedure, in which the energetic positions and intensities of the theoretical bands were optimized. Besides providing a basis for a refined analysis of the spectrum, the fit allows us to assess the accuracy of the calculation. As expected for this level of theory, the absolute accuracy of the valence CI energies is found to be about 0.3 eV. The inherent error of the one-centre transition rates is less than 5% of the most intense transition in the spectrum. The frequently questioned one-centre Auger transition rates are shown to be rather appropriate if applied with reasonable wavefunctions and if the vibrational band structure of the molecular spectrum is properly taken into account.

Place, publisher, year, edition, pages
2008. Vol. 41, no 12, 125101- p.
National Category
Physical Sciences
URN: urn:nbn:se:uu:diva-96986DOI: 10.1088/0953-4075/41/12/125101ISI: 000257177700004OAI: oai:DiVA.org:uu-96986DiVA: diva2:171744
Available from: 2008-04-03 Created: 2008-04-03 Last updated: 2009-10-29Bibliographically approved
In thesis
1. Synchrotron Radiation Studies of Free and Adsorbed Molecules
Open this publication in new window or tab >>Synchrotron Radiation Studies of Free and Adsorbed Molecules
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis contains two parts. The first part concerns the research work on free molecules using synchrotron-radiation-related techniques. Auger electron spectra of two free open-shell molecules, O2 and NO, were studied experimentally and theoretically. Photoionization experimental technique with tunable synchrotron radiation source was used to induce core-level electron ionization and obtain the KVV normal Auger electron spectra. A quantitative assignment of O2 normal Auger spectrum was obtained by applying ab initio CI calculations and LVI Auger line shape simulations including the bond length dependence of Auger transition rates. The photon energy dependence of normal Auger electron spectra was focused on with photon energies in the vicinities of core-ionization threshold energies. Consequently, the MAPCI (Molecular Auger Post Collision Interaction) theory was developed. Taking the near-threshold O2 normal Auger spectrum as an example, the two extreme cases of MAPCI effect, “atomic-like PCI” and “molecular PCI”, were discovered and discussed. The effect of shape resonance on near-threshold molecular normal Auger spectrum was discussed taking NO near threshold normal Auger spectra as example.

The second part deals with research work on the chemisorption of small epoxy organic molecules, ethylene oxide, methyl oxirane, on Si (100) surfaces. Synchrotron radiation related techniques, UPS, XPS and NEXAFS, were applied. Based on the valence photoemission spectra, C 1s and Si 2p XPS spectra, the epoxy ring opening reactions of these molecules in chemisorption process were proved. Further tentative search for the surface-adsorbate CDAD effect was performed, and no evident circular dichroism was confirmed.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2008. xiv, 55 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 420
Physics, Synchrotron radiation, Auger electron spectroscopy, one-step model, Post Collision Interaction (PCI), theoretical modeling, molecules, adsorbates, UPS, XPS, XAS, NEXAFS, Fysik
urn:nbn:se:uu:diva-8610 (URN)978-91-554-7150-7 (ISBN)
Public defence
2008-04-25, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15
Available from: 2008-04-03 Created: 2008-04-03Bibliographically approved

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