Rydberg spectroscopy of single-electron capture in low-energy collisions of Ar9+ and Ar8+ with cesium

Optical spectroscopy has been used to study electron capture into Ar{sup 9+} and Ar{sup 8+} ions from cesium at several impact energies of between 8 and 180 keV. Many Rydberg lines were observed. At high spectral resolution the quasi-{ital l}-degeneracy of final Rydberg states was removed and the fine-structure components of doubly excited Rydberg transitions were resolved. Cross sections for state-selective electron capture in collision of Ar{sup 8+} with cesium were determined and then compared with theoretical data calculated by means of a three-body classical-trajectory Monte Carlo method and with predictions of a classical barrier model.