Berlin 2001 – wissenschaftliches Programm
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AMPD: EPS AMPD
AMPD 6: Sitzung 6
AMPD 6.1: Vortrag
Mittwoch, 4. April 2001, 09:00–09:35, H104
Negative–ion experiments at the storage rings in Aarhus — •P. Balling — Institute of Physics and Astronomy, University of Aarhus, DK-8000 Aarhus C, Denmark
The experimental investigations of negative ions have matured with the technological developments of lasers and ultra–high vacuum. In particular, recent results have demonstrated that the use of heavy–ion storage rings allows detailed studies of new aspects of negative–ion physics. This talk will offer a selection of experiments recently performed at the ASTRID and ELISA storage rings in Aarhus, Denmark. There are at present three main negative–ion programs: Measurements of lifetimes for metastable atomic and molecular negative ions, electron–ion collision experiments with merged beams at low relative energy, and high–resolution vacuum–ultraviolet spectroscopy of H−.
Shortly after the successful storage of stable negative ions in ASTRID, it was demonstrated that the storage ring was a unique tool for measuring the lifetimes of long–lived metastable atomic-negative-ion states. Recently, the studies have been extended to a selection of small molecular–negative–ion systems [1,2]. The establishment of the compact electrostatic storage ring ELISA has permitted a re–investigation of the fundamental He− system [3]. In particular, the ability to cool the entire ring structure allowed a study of the role of black–body–radiation–induced photodetachment. This feature was also employed in a measurement of the extremely long lifetime of H2CC−, the vinylidene anion [4].
The formation of doubly–charged negative ions has been the subject of considerable theoretical and experimental interest. In particular, merged-beams experiments at heavy-ion storage rings have permitted the observation of short–lived dianionic states in small molecules [5–7]. A recent investigation of the triatomic molecular ion NO2− (nitrite) demonstrated that some systems exhibit more than one short–lived dianionic state [8].
The negative hydrogen ion represents an important three–body system in atomic physics. Theoretical treatments of various aspects of the system are numerous, but the experimental investigations are scarcer. An experimental program at the ASTRID storage ring has been devoted to laser–spectroscopic investigations of the resonance region near the n=2 threshold (see [9,10] and references herein). Velocity tuning of the ions into resonance has allowed the use of a fixed-frequency light source and thus facilitated tunable spectroscopy in the vacuum–ultraviolet region. In addition, the application of electron cooling has permitted very high photon–energy resolution. This has recently allowed the extraction of accurate resonance parameters [10]. The talk will include a new, unpublished reinvestigation of the broad resonance just above the n=2 threshold.
[1] T. Andersen et al., Phys. Rev. A 60, 3627 (1999).
[2] M. K. Raarup et al., J. Phys. B 32, L659 (1999).
[3] U. V. Pedersen et al., submitted to Phys. Rev. A (2001).
[4] M. J. Jensen et al., Phys. Rev. Lett. 84, 1128 (2000).
[5] L. H. Andersen et al., J. Phys. B 29, L643 (1996).
[6] H. B. Pedersen et al., Phys. Rev. Lett. 81, 2667 (1998).
[7] H. B. Pedersen et al., Phys. Rev. A 60, 2882 (1999).
[8] L. H. Andersen et al., J. Chem. Phys. 114, 147 (2001).
[9] P. Balling et al., Phys. Rev. A 61, 022702 (2000).
[10] M. K. Raarup et al., Phys. Rev. Lett. 85, 4028 (2000).