| 1. |
- Brandefelt, Nicklas, et al.
(författare)
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4S resonances of He-below the He+(n=1) threshold
- 1999
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Ingår i: Physical Review A. - : American Physical Society. - 1050-2947. ; 59, s. 2691-2696
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Tidskriftsartikel (refereegranskat)abstract
- 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
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| 2. |
- Brandefelt, Nicklas, 1971-
(författare)
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Resonant States in Negative Ions
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 3. |
- Brandefelt, Nicklas, et al.
(författare)
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Triply excited 4S resonances of He-
- 2002
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Ingår i: Physical Review A. - : American Physical Society. - 1050-2947. ; 65:3, s. 032503-032510
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Tidskriftsartikel (refereegranskat)abstract
- Resonances of 4Se symmetry in He- are searched for in the region above the He+(n=1) threshold and below the He+(n=2) 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 decay channels. Seven resonances are found and five are presented with energy position and width
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| 4. |
- Bürgers, Andre, et al.
(författare)
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The interelectronic angle in doubly excited states and the quality of approximate quantum numbers
- 1998
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Ingår i: Journal of Physics B: Atomic, Molecular and Optical Physics. - Washington D.C. : Institute of Physics. - 0953-4075 .- 1361-6455. ; 31, s. 3181-3198
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Tidskriftsartikel (refereegranskat)abstract
- We present complex scaling calculations of the cosine of the interelectronic angle in doubly excited states of helium below the N = 4 threshold. Since it is directly connected to one of the approximate quantum numbers commonly used to classify doubly excited states, an analysis of this expectation value will give information about the quality of this quantum number. Deviations from the predicted value already occur in the lowest manifold of resonances and are interpreted as a mixture of different basis states. This assertion is tested by a direct doubly excited symmetry basis expansion. Two types of mixing are observed; mixing of basis states to form Rydberg series and mixing of Rydberg series converging to the same threshold. As a possible origin of the basis state mixing which affects the Rydberg series as a whole, avoided crossings in the variation of the resonance energies with respect to the nuclear charge Z are discussed. Mixing between Rydberg series is due to close degeneracies in the resonance energies and connected with avoided crossings in the quantum defect. Both types can easily be distinguished by regarding real and imaginary parts of the complex expectation value
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| 5. |
- Haeffler, Gunnar, et al.
(författare)
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Strongly correlated states in the Li- ion
- 2001
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Ingår i: Physical Review A. - : American Physical Society. - 1050-2947. ; 63:5, s. 053409-053412
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Tidskriftsartikel (refereegranskat)abstract
- A collinear laser-ion beam apparatus has been used to investigate resonance structure in the Li(3s)+e-(kp) partial photodetachment cross section below the Li(6p) threshold. A complex rotation calculation was used to identify the strongly correlated, doubly excited states of the quasi-two-electron ion Li- that are responsible for the observed resonances. These represent the most highly excited states of Li- observed thus far. Several members of a strong “+” type series were observed as well as at least one resonance with “-” type character. In particular, we report on an observation of a resonance that violates the Δν=0 propensity rule.
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