Electron Collisional Broadening of Isolated Lines from Multiply-Ionized Atoms
Recent experimental and theoretical (both improved semiclassical and fully quantum-mechanical) results for B III and Ne VII delta n = 0 transitions with n = 2 or 3, respectively, are discussed. The probable reasons for disagreements by about a factor of 2 between the fully quantum-mechanically calculated and both measured and semiclassically calculated widths can be explained in terms of violation of validity criteria and non-thermal Doppler effects. More independent determinations of line widths for multiply-ionized non-hydrogenic ions are called for, but meanwhile caution should be exercised in the use of corresponding semiclassically calculated widths, e.g., in opacity calculations or for plasma density diagnostics. Only the quantum calculations allow a clear separation of elastic and inelastic scattering contributions to the width. For B III, elastic scattering contributes about 30% whereas for Ne VII inelastic scattering dominates. This allows rather direct comparisons with benchmark electron-ion scattering experiments.