Velocity dependence of single-electron capture for the 0.4-5-keV/amu Ar8+-Cs(6s) collision system

The single-electron capture (SEC) process which occurs in Ar⁸⁺-Cs(6s) collisions is experimentally studied, in the 0.4-5-keV/amu energy range, by optical spectroscopy in the near UV and visible wavelength range (200-600 nm). The classical-trajectory Monte Carlo (CTMC) method is also used to determine the state-selective electron-capture cross sections. For high collision energies, strong lines corresponding to Δn=1-4 transitions from n=7 to 13 states with large angular momentum values of Ar VIII and Δn=0 transitions from n=5 states are observed. For low collision energies, together with the lines observed for high collision energies, lines corresponding to transitions from states with low-l values (10s, 11s, and 13s) are detected. Production cross sections for the most populated levels (n=9, 10, and 11) are determined and compared with the previous experimental data of Martin et al. [Phys. Rev. A 46, 1316 (1992)] and Denis et al. [Phys. Rev. A 50, 2263 (1994)], and with the CTMC calculations. From molecular structure calculations which are performed for the \{Ar⁷⁺+Cs\}⁺ molecular system, our results are analyzed in terms of dynamical couplings between the relevant molecular channels involved in the electron-capture process. Polarization degrees for SEC lines corresponding to transitions between high-l values states are also measured. The comparison with those calculated from the CTMC results provides information about the Zeeman sublevel distributions.