Probing the dynamics of electron correlation with charged particles and photons

Double ionization of helium in collisions with photons and fast charged particles will be discussed in terms of mechanisms for the two electron process which give a picture of the dynamics of electron correlation. In fast collisions it is the electron-electron correlation interaction which is usually responsible for the second electron transition. In general scattering by photons is understood, but scattering by charged particles is not well understood. Although Compton scattering (C) by photons and scattering by fast charged particles (Z) are different processes with different interaction potentials they may both be expressed in first order perturbation theory in terms of the same matrix element, < f|eiQ·r|i >, the atomic form factor. This means that at a fixed value of the momentum transfer, Q, data for charged particle scattering may be related to data for Compton scattering. For small Q both of these processes may be related to the usual dipole cross section for photoannhilation (PE). Relations between the ratio of single to double ionization by photoannihilation, by Compton scattering and by impact of charged particles will be discussed