Population of high-Lsulfur Rydberg levels by ion–Rydberg-atom charge exchange

A fast beam of sulfur Rydberg atoms is formed by charge exchange from an 11-keV beam of ${\mathrm{S}}^{+}$ ions in a crossed thermal rubidium beam, laser-excited to the 10F or 8F levels. Population of specific n=9,10 sulfur Rydberg levels is studied by selective excitation with a Doppler-tuned ${\mathrm{CO}}_2$ laser followed by field ionization. Complete spectral resolution of levels with L≥4 allows a direct study of the populations in specific nL levels and reveals distinctly nonstatistical distributions of population in L. The results are compared with predictions of a classical Monte Carlo three-body collision theory, revealing some similarities, but also clear differences.