Electron-impact excitation of multicharged ions: Merged beams experiments

Electron-impact excitation cross sections for several multicharged ions have been measured near threshold using the merged electron-ion beams energy loss (MEIBEL) technique. This technique allows the investigation of optically-allowed and forbidden transitions with sufficient energy resolution, typically about 0.2 eV, to resolve resonance structures in the cross sections. Results from the JILA/ORNL MEIBEL experiment on allowed transitions in several multicharged ions demonstrate the ability of various theoretical methods to predict cross sections in the absence of resonances. Comparisons of R-matrix calculations and measured cross sections for transitions in Mg-like Si2+ and Ar6+, however, indicate that theory must continue to evolve in order to more accurately predict cross sections involving significant contributions from dielectronic resonances and interactions between neighboring resonances. copyright 1999 American Institute of Physics