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Double Excitations of Helium in Weak Static Electric Fields
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics II.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
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2006 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 96, 043002- p.Article in journal (Refereed) Published
Abstract [en]

A dramatic electric field dependence has been observed in the fluorescence yield spectrum of the doubly excited states in helium, where a rich phenomenology is encountered below the N=2 threshold. Fluorescence yields of certain states can be tuned to zero, while other dipole-forbidden states are significantly enhanced, for fields much weaker than 1  kV/cm. Using an R-matrix multichannel quantum defect theory, spherical-to-parabolic frame transformation method, we are able to reproduce the main features of the observed spectrum, and we discuss the qualitative behavior in terms of weak electric field mixing.

Place, publisher, year, edition, pages
2006. Vol. 96, 043002- p.
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-94517DOI: 10.1103/PhysRevLett.96.043002OAI: oai:DiVA.org:uu-94517DiVA: diva2:168390
Available from: 2006-05-05 Created: 2006-05-05 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Double Excitations in Helium Atoms and Lithium Compounds
Open this publication in new window or tab >>Double Excitations in Helium Atoms and Lithium Compounds
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis addresses the investigation of doubly excited 2l´nl states in helium atoms and double core excitations in solid lithium compounds.

Measurements on He are made in field free environments and under the influence of electric and magnetic fields, using synchrotron based inelastic photon scattering. Cross sections for scattering to singly excited final states are directly determined and compared to theoretical results and are found to be in excellent agreement. Radiative and spin-orbit effects are quantified and are shown to play an important role in the overall characterization of highly excited He states below the N =2 threshold. A dramatic electric field dependence is also observed in the flourecence yield already for relatively weak fields. This signal increase, induced by electric as well as magnetic fields, is interpreted in terms of mixing with states of higher fluorescence branching ratios.

Double core excitations at the lithium site in solid lithium compounds are investigated using resonant inelastic x-ray scattering (RIXS). The lithium halides LiF, LiCl, LiBr and LiI are studied as well as the molecular compounds Li2O, Li2CO3 and LiBF4. States with one, as well as both, of the excited electrons localized at the site of the bare lithium nucleus are identified, and transitions which involve additional band excitations are observed. A strong influence of the chemical surrounding is found, and it is discussed in terms of the ionic character of the chemical bond.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2006. 114 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 186
Keyword
Atomic and molecular physics, Soft X-ray emission, resonant inelastic X-ray scattering, double excitations, lithium halide, helium, Atom- och molekylfysik
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-6889 (URN)91-554-6572-2 (ISBN)
Public defence
2006-05-26, Polhelmsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15
Opponent
Supervisors
Available from: 2006-05-05 Created: 2006-05-05 Last updated: 2016-04-21Bibliographically approved

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