High-resolution excitation functions in the threshold region

A brief description is given of the experimental investigations concerning threshold and resonance phenomena in the electron-impact excitation of atoms. Experiments of this kind are usually restricted to the excitation of low-n levels, where the short range interactions dominate. Electron-electron correlations become progressively more important for the near-threshold excitation of high-n states. Classical predictions for the electron-impact processes leading to single and double Rydberg electrons in high-n orbitals are obtained by applying a new generalisation procedure to the Wannier's threshold ionization formula. 15 refs.; 12 figs