Radiative electron capture: a tool for structure studies of heavy few-electron ions

Radiative Electron Capture (REC) in collisions of hydrogenic germanium ions with hydrogen is measured for projectile energies between 4 and 12 MeV/u. Extrapolating the resulting centroid energies of the K-REC radiation to zero collision velocity theK-binding energy in helium-like germanium-ions is determined. The value compares well with the theoretical prediction. REC in atomic collisions is advertised as a spectroscopic tool for structure investigations of very heavy few-electron projectiles.     

Bicovariant differential calculi on Sμ U(2)

Bicovariant, differential calculi on S U(2) are investigated and the nonexistence of three-dimensional calculus and the uniqueness of 4D_± calculi are proved. Formulae for the external product, external derivative, and classical limit are presented.     

Photon angular distribution of Radiative Electron Capture into the M shell of He-like uranium ions at 110–140 MeV/u

Measurements of the photon angular distribution of Radiative Electron Capture into the M shell have been performed with He-like uranium ions in the range 110–140 MeV/u. In addition, L REC was studied at a projectile energy of 140 MeV/u. In both cases, the experimental data show an asymmetry around 90° and agree well with a fully relativistic theory.     

Precise determination of the 2s(1/2)-2p(1/2) splitting in very heavy lithiumlike ions utilizing dielectronic recombination

The 2s(1/2)-2p(1/2) energy splittings DeltaE(L) of the lithiumlike ions 19779Au76+, 20882Pb79+, and 23892U89+ have been measured at the Experimental Storage Ring, utilizing low energy dielectronic recombination. The resonance energies in total 41 different 1s(2) 2p(1/2)nl(j(')) (n > or =20) autoionizing Rydberg states populated in the dielectronic capture process have been determined. The 2s(1/2)-->2p(1/2) excitation energies have been obtained by extrapolation of these resonance energies to the associated series limits n--> infinity. The combined analysis of the experimental data for all three ions yields DeltaE(L)=216.134(96) eV for Au76+, 230.650(81) eV for Pb79+, and 280.516(99) eV for U89+.     

The unusual strenght of the 5.14 → 1.27 MeV, 2− → 2+, transition in 22Ne

The lifetime of the 5.14 MeV excited state of ²²Ne was investigated by use of the electronic timing, recoil distance and Doppler shift attenuation techniques. A mean life τ = 1.2±0.3 ps was obtained, corresponding to a transition strenght of 9.8 × 10^?6W.u. for the El decay of this state.     

Recombination of U 92 + ions with electrons

Recombination of fully stripped U⁹²⁺ ions with electrons has been investigated at the Experimental Storage Ring (ESR) in Darmstadt. Absolute recombination rate coefficients have been measured for relative energies from 0 to 33 eV. For energies greater than 20 meV the experimental result is well described by the theory for radiative recombination (RR). Below 20 meV the experimental rate increasingly exceeds the RR calculation as observed previously in the recombination of light bare ions as well as of Bi⁸³⁺. This low-energy rate enhancement is shown to scale as Z^2.6 for bare ions, where Z is the atomic number of the ion. The U⁹²⁺ recombination rate enhancement is insensitive to changes of the electron density. Variation of the magnetic guiding field strength from 80 mT to 120 mT resulted in oscillations of the recombination rate at 0 eV. The oscillations are partly attributed to changes of the transverse electron temperature accompanying the change of the magnetic guiding field strength; partly they may be caused by uncompensated small changes of the interaction angle between the two beams. Received 1st March 2001 and Received in final form 20 April 2001     

Probing the Coordination Environment of the Human Copper Chaperone HAH1: Characterization of HgII‐Bridged Homodimeric Species in Solution

Although metal ion homeostasis in cells is often mediated through metallochaperones, there are opportunities for toxic metals to be sequestered through the existing transport apparatus. Proper trafficking of Cu^I in human cells is partially achieved through complexation by HAH1, the human metallochaperone responsible for copper delivery to the Wilson and Menkes ATPase located in the trans‐Golgi apparatus. In addition to binding copper, HAH1 strongly complexes Hg^II, with the X‐ray structure of this complex previously described. It is important to clarify the solution behavior of these systems and, therefore, the binding of Hg^II to HAH1 was probed over the pH range 7.5 to 9.4 using ¹⁹⁹Hg NMR, ^199mHg PAC and UV–visible spectroscopies. The metal‐dependent protein association over this pH range was examined using analytical gel‐filtration. It can be concluded that at pH 7.5, Hg^II is bound to a monomeric HAH1 as a two coordinate, linear complex (HgS₂), like the Hg^II–Atx1 X‐ray structure (PDB ID: 1CC8). At pH 9.4, Hg^II promotes HAH1 association, leading to formation of HgS₃ and HgS₄ complexes, which are in exchange on the μs–ns time scale. Thus, structures that may represent central intermediates in the process of metal ion transfer, as well as their exchange kinetics have been characterized.