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4S resonances of He-below the He+(n=1) threshold
Stockholm University, Faculty of Science, Department of Physics.
1999 (English)In: Physical Review A, ISSN 1050-2947, Vol. 59, 2691-2696 p.Article in journal (Refereed) Published
Abstract [en]

Resonances of 4Se symmetry in He- are searched for in the region below the He+(n=1) threshold. The energies and widths of the resonances are calculated with an ab initio three-electron description of the ion. The complex rotation method is combined with the use of B splines in a spherical cavity to describe the ion and the decaying channels. Four resonances are found. The first three resonances agree well with experiments. The fourth resonance has not been seen in an experiment yet, due to a small photodetachment cross section and large width

Place, publisher, year, edition, pages
American Physical Society , 1999. Vol. 59, 2691-2696 p.
National Category
Physical Sciences
Research subject
URN: urn:nbn:se:su:diva-23231DOI: 10.1103/PhysRevA.59.2691OAI: diva2:190832
Part of urn:nbn:se:su:diva-199Available from: 2001-08-22 Created: 2001-08-22 Last updated: 2010-01-05Bibliographically approved
In thesis
1. Resonant States in Negative Ions
Open this publication in new window or tab >>Resonant States in Negative Ions
2001 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Resonant states are multiply excited states in atoms and ions that have enough energy to decay by emitting an electron. The ability to emit an electron and the strong electron correlation (which is extra strong in negative ions) makes these states both interesting and challenging from a theoretical point of view. The main contribution in this thesis is a method, which combines the use of B splines and complex rotation, to solve the three-electron Schrödinger equation treating all three electrons equally. It is used to calculate doubly excited and triply excited states of 4S symmetry with even parity in He-. For the doubly excited states there are experimental and theoretical data to compare with. For the triply excited states there is only theoretical data available and only for one of the resonances. The agreement is in general good. For the triply excited state there is a significant and interesting difference in the width between our calculation and another method. A cause for this deviation is suggested. The method is also used to find a resonant state of 4S symmetry with odd parity in H2-. This state, in this extremely negative system, has been predicted by two earlier calculations but is highly controversial.

Several other studies presented here focus on two-electron systems. In one, the effect of the splitting of the degenerate H(n=2) thresholds in H-, on the resonant states converging to this threshold, is studied. If a completely degenerate threshold is assumed an infinite series of states is expected to converge to the threshold. Here states of 1P symmetry and odd parity are examined, and it is found that the relativistic and radiative splitting of the threshold causes the series to end after only three resonant states. Since the independent particle model completely fails for doubly excited states, several schemes of alternative quantum numbers have been suggested. We investigate the so called DESB (Doubly Excited Symmetry Basis) quantum numbers in several calculations. For the doubly excited states of He- mentioned above we investigate one resonance and find that it cannot be assigned DESB quantum numbers unambiguously. We also investigate these quantum numbers for states of 1S even parity in He. We find two types of mixing of DESB states in the doubly excited states calculated. We also show that the amount of mixing of DESB quantum numbers can be inferred from the value of the cosine of the inter-electronic angle. In a study on Li- the calculated cosine values are used to identify doubly excited states measured in a photodetachment experiment. In particular a resonant state that violates a propensity rule is found.

Place, publisher, year, edition, pages
Stockholm: Fysikum, 2001. 60 p.
Molekylfysik, Atomfysik, Kärnfysik, Partikelfysik
National Category
Atom and Molecular Physics and Optics
urn:nbn:se:su:diva-199 (URN)91-7265-309-4 (ISBN)
Public defence
2001-09-12, Sal FB52, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:00
Available from: 2001-08-22 Created: 2001-08-22Bibliographically approved

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