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Abstract

Stored fast ion beams in atomic and molecular collision experiments are discussed with an emphasis on electron-ion interactions at low relative energies. Recent progress was obtained in electron collision spectroscopy using an electron-cooled stored ion beam and a separate electron target in the same storage ring; from a cryogenic photocathode, electron beams with internal temperatures of 5 to 10 K were produced. Results are presented for dielectronic recombination resonances, resolving the hyperfine structure of stored lithiumlike scandium ions and obtaining precise results for the fine structure splitting of these ions, and for ro-vibrational resonances in the recombination of electrons with hydrogen molecular ions, revealing sharp structures down to 2 meV. An overview of the cryogenic storage ring (CSR) project in Heidelberg is given.