The Close-Coupling Methods Applied to Photoionisation of Neutral Atoms and Positive Ions

Abstract

As Professor Fano and Dr. Inokuti mentioned it in their lectures, close-coupling functions are usually used to describe the electron scattering process. But. such continuum wave functions can describe both an ion scattering an electron (calculations of electron impact cross sections) and the final states appropriate to photoionisation. However, close-coupling functions have only been introduced recently in the calculation of photoionisation cross sections at low energies: it was only in 1967 that Henry and Lipsky¹ provided an exact formulation of the photoionisation process within the framework of the dipole approximation, in LS coupling, when the coupling between the final state channels was introduced. In this talk, I will essentially develop three points. First, I shall recall briefly how the close-coupling equations are derived in the scattering process formulation; second, I shall show how the close-coupling continuum wave functions of the scattering process can be introduced in multichannel photoionisation. Then, I shall emphasize those methods of solving the close-coupling equations which have been used to write the recently available computer codes for the calculation of electron scattering and photoionisation cross sections of atomic systems.