PHOTOEXCITATION AND IONIZATION IN HELIUM - ZERO-KINETIC-ENERGY SPECTROSCOPY

The cross sections for double and single photoexcitation and -ionizati on of helium are calculated in the acceleration gauge assuming a total ly asymmetric energy and angular momentum partitioning between two ele ctrons. The electron-electron correlation is taken, into account in th e ground-state wave function. By extrapolating single-ionization diffe rential oscillator strengths to n --> infinity, where n is the excited He+ principal quantum number, an estimate of the double-ionization cr oss sections is obtained. Comparison with other calculations is made.