Low-energy collisions of Rydberg atom-ion systems are investigated theoretically. We present the parameter space associated with suitable approaches for the dynamics of Rydberg atom-ion collisions, i.e., quantum, Langevin, and classical exchange regimes, showing that for the lowest reachable temperatures a classical treatment is appropriate. A quasiclassical trajectory method is used to study charge exchange cross sections for ${\mathrm{Li}}^{*}\text{\ensuremath{-}}{\mathrm{Li}}^{+}$ and ${\mathrm{Li}}^{*}\text{\ensuremath{-}}{\mathrm{Cs}}^{+}$ at collision energies down to
1K. For cold collisions we find the charge exchange cross section deviating from the
n4 geometric scaling. Furthermore, for low-energy collisions, we find both an influence of the ionic core repulsion as well as variations for two different models used for describing the electron-core potential.
List of contributors Preface 1. Rydberg atoms in astrophysics A. Dalgarno 2. Theoretical studies of hydrogen Rydberg atoms in electric fields R. J. Damburg and V. V. Kolosov 3. Rydberg atoms in strong fields D. Kleppner, Michael G. Littman and Myron L. Zimmerman 4. Spectroscopy of one- and two-electron Rydberg atoms C. Fabre and S. Haroche 5. Interaction of Rydberg atoms with blackbody radiation T. F. Gallagher 6. Theoretical approaches to low-energy collisions of Rydberg atoms with atoms and ions A. P. Hickman, R. E. Olson and J. Pascale 7. Experimental studies of the interaction of Rydberg atoms with atomic species at thermal energies F. Gounand and J. Berlande 8. Theoretical studies of collisions of Rydberg atoms with molecules Michio Matsuzawa 9. Experimental studies of thermal-energy collisions of Rydberg atoms with molecules F. B. Dunning and R. F. Stebbings 10. High-Rydberg molecules Robert S. Freund 11. Theory of Rydberg collisions with electrons, ions and neutrals M. R. Flannery 12. Experimental studies of the interactions of Rydberg atoms with charged particles J. -F. Delpech 13. Rydberg studies using fast beams Peter M. Koch Index.