A study of the two-electron Fourier amplitudes of atomic and molecular wavefunctions using the (γ,2e) and (e,3e) processes at high energies

A study of the angular correlations, using the coincidence technique, of two (three) fast final electrons in the process of double ionisation of atoms by photons (electrons) provides direct information on the two-electron Fourier amplitudes. These specify directly, and with a high sensitivity, the electron-electron Coulomb correlations in the initial wavefunction projected on a given state of the final ion. These double Fourier spectra are considered in the orthogonalised plane-wave approximation using a helium atom as an example. Cross sections for various types of initial-state wavefunctions including the 'exact' functions of Hylleraas and of Byron and Joachain (1967) have been calculated.