Referierte Publikationen

In collisions between highly charged, heavy ions and light target atoms at adiabaticity parameters of 0.5 less-than-or-equal-to v2/u2 less-than-or-equal-to 0.75, resonant transfer and excitation (RTE) is an important charge-exchange process. Experiments for medium Z-ions are reviewed. Special emphasis is given to the competing radiative electron capture (REC) process. The general dependences of REC are discussed. In particular, we elucidate results obtained by the triple X-ray/X-ray/charge-changed particle coincidence technique for hydrogenic projectiles up to 36Kr35+ ions. With this method we could isolate a single RTE resonance, the 2s2p1P1 state, which stabilizes radiatively to the metastable 1s2s1S0 state. This state can only decay via two photon emission (2E1). Applying the triple coincidence technique we observed additional strong photon coincidences induced by cascades following REC into high projectile states.

The doubly excited 2s2p 1P1 level of Kr34+ populated via resonant transfer and excitation (RTE) feeds selectively the metastable 1s2s 1S0 state which can only decay via simultaneous emission of two photons to the ground state 1s2 1S0. X-ray/X-ray coincidence measurements in heavy ion-atom collisions enable the direct measurement of the spectral distribution of the two-photon decay in He-like ions. In addition, we observe strong photon cascades induced by radiative electron capture.

Evidence for resonant two-electron capture and excitation, i.e. the time-recersed double Auger process with radiative stabilitization, was found by measuring coincidences between two K-X-rays of a heavy ion associated with its double charge exchange. Hydrogen-like Ge31+ ions with energies of 4.5-11.5 MeV/u were directed into a neon gas target. Contributions from the double non-resonant transfer and excitation process are also discussed.

For non-naked highly-charged heavy ions, dielectronic recombination (DR) can be the dominant electron capture process. Depending on the kind of a DR resonance involved, cross sections may reach values up to 10^2-18 cm^2 at the peak maximum. The widths of the DR resonances are typically <1 eV. Tuning a merged electron beam with an internal temperature typically - 0.1 eV to the DR resonance, a well defined narrow part can be cut out of the original "hot" primary ion beam by this charge-exchange process. The charge-changed new beam is pretty "cool" (DE/E=10^-5). Acase study for Ge^31+ +e=Ge^30+** (2P^2^1D_2) is given. Technical applications of DR beam tailoring techniques at heavy-ion storage rings will be discussed.