Velocity dependence of single-electron capture for the 0.4–5-keV/amu Ar 8 + − Cs ( 6 s ) collision system

The single-electron capture (SEC) process which occurs in ${\mathrm{Ar}}^{8+}$-$\mathrm{Cs}(6s)$ 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 $\ensuremath{\Delta}n=1$--4 transitions from $n=7$ to 13 states with large angular momentum values of Ar VIII and $\ensuremath{\Delta}n=0$ 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 ${{\mathrm{Ar}}^{7+}+\mathrm{Cs}{}}^{+}$ 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.