Dielectronic recombination (DR) of xenonlike W20+ forming W19+ has been
studied experimentally at a heavy-ion storage-ring. A merged-beams method has
been employed for obtaining absolute rate coefficients for electron-ion
recombination in the collision energy range 0-140 eV. The measured rate
coefficient is dominated by strong DR resonances even at the lowest
experimental energies. At plasma temperatures where the fractional abundance of
W20+ is expected to peak in a fusion plasma, the experimentally derived plasma
recombination rate coefficient is over a factor of 4 larger than the
theoretically-calculated rate coefficient which is currently used in fusion
plasma modeling. The largest part of this discrepancy stems most probably from
the neglect in the theoretical calculations of DR associated with
fine-structure excitations of the W20+([Kr] 4d10 4f8) ion core.Comment: 7 pagers, 4 figures, accepted for publication in Physical Review
In chemistry and biology, chirality, or handedness, refers to molecules that exist in two spatial configurations that are incongruent mirror images of one another. Almost all biologically active molecules are chiral, and the correct determination of their absolute configuration is essential for the understanding and the development of processes involving chiral molecules. Anomalous x-ray diffraction and vibrational optical activity measurements are broadly used to determine absolute configurations of solid or liquid samples. Determining absolute configurations of chiral molecules in the gas phase is still a formidable challenge. Here we demonstrate the determination of the absolute configuration of isotopically labeled (R,R)-2,3-dideuterooxirane by foil-induced Coulomb explosion imaging of individual molecules. Our technique provides unambiguous and direct access to the absolute configuration of small gas-phase species, including ions and molecular fragments.
We present experimentally measured and theoretically calculated rate coefficients for the electron-ion recombination of W 18+ ([Kr]4d 10 4f 10) forming W 17+. At low electron-ion collision energies, the merged-beam rate coefficient is dominated by strong, mutually overlapping recombination resonances. In the temperature range where the fractional abundance of W 18+ is expected to peak in a fusion plasma, the experimentally derived Maxwellian recombination rate coefficient is 5 to 10 times larger than that which is currently recommended for plasma modeling. The complexity of the atomic structure of the open-4f system under study makes the theoretical calculations extremely demanding. Nevertheless, the results of the present Breit-Wigner partitioned dielectronic recombination calculations agree reasonably well with the experimental findings. This also gives confidence in the ability of the theory to generate sufficiently accurate atomic data for the plasma modeling of other complex ions.
We have performed measurements of the dissociative electron recombination (DR) of H + 3 at the ion storage ring TSR utilizing a supersonic expansion ion source. The ion source has been characterized by continuous wave cavity ring-down spectroscopy. We present high-resolution DR rate coefficients for different nuclear spin modifications of H + 3 combined with precise fragment imaging studies of the internal excitation of the H + 3 ions inside the storage ring. The measurements resolve changes in the energy dependence between the ortho-H + 3 and para-H + 3 rate coefficients at low center-of-mass collision energies. Analysis of the imaging data indicates that the stored H + 3 ions may have higher rotational temperatures than previously assumed, most likely due to collisional heating during the extraction of the ions from the ion source. Simulations of the ion extraction shed light on possible origins of the heating process and how to avoid it in future experiments.
Lifetimes of 3s23pk ground configuration levels of Al-, Si-, P- and S-like ions of Fe, Co and Ni have been measured at a heavy-ion storage ring. Some of the observed decay curves show strong evidence of cascade repopulation from specific 3d levels that feature lifetimes in the same multi-millisecond range as the levels of the ground configuration. We identify the foil-stripping process in the ion production as the cause of the cascade level population and assess the importance of specific cascades for the measurement technique.
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