RADIATIVE RECOMBINATION WITH HIGHLY CHARGED SI6+ AND SI11+ IONS

The rate coefficient <v-sigma> for radiative recombination between free electrons and highly charged Si6+ and Si11+ ions has been measured in the energy region from 0 to 1 eV. The experimental results were obtained with a merged-beams technique. Knowledge about the relative velocity distribution allowed a direct comparison with theory. It was found that for Li-like Si11+, the effective charge to be used in a calculation developed for bare ions is the total ion charge, Z(eff) almost-equal-to 11. This is in agreement with earlier findings for H-like ions and other Li-like ions. For O-like Si6+, the effective charge is found to be Z(eff) almost-equal-to 9. For Si6+, the measured rate coefficient is more than a factor of two larger than calculations based on the total ion charge (Z(eff) = 6). This shows evidence for significant incomplete screening in the case of Si6+.