Projectile velocity dependence of emission line polarization degrees following slow Ar8+-Li(2s) state-selective electron-capture collisions

The influence of the projectile velocity on the m(l) distributions of the Ar7+ excited states produced by electron capture during Ar8+-Li(2s) collisions is studied experimentally between 1.5 and 4.5 keV amu(-1) by measuring the polarization of the emitted light, and theoretically between 1 and 4 keV amu(-1) by using the classical trajectory Monte Carlo (CTMC) method. We investigate the 7l'-8l and 8l'-9l radiative transitions subsequent to the decay of the 8l and 9l sublevels of Ar VIII, which are preferentially populated by the single electron capture process. A small but not negligible effect is seen for the experimental polarization ratios relating to transitions from sublevels of large l values, showing a slight increase of the component parallel to the incident ion beam as the projectile energy increases. Theoretical polarization ratios obtained from CTMC calculated m(l) distributions are in excellent agreement with the measured polarization ratios. Electronic energy curve calculations are then presented in order to discuss these results in terms of dynamical couplings.