A derivation is given of the exact form of the three-body Coulomb wavefunction in the asymptotic region where the separation of all particles tends to infinity. Using a modification of the method of Pluvinage, an approximate three-body scattering wavefunction is derived that satisfies this boundary condition. Triply-differential cross sections (rocs) for electron impact ionisation of atomic hydrogen calculated with this scattering wavefunction, which contains no free parameters, show excellent agreement with measurements at impact energies greater than 150 eV. The corresponding TDCS for positron impact ionisation are also presented.

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A rather complete understanding is emerging of the process of full fragmentation of the helium atom following absorption of a single photon. In this review the major experimental and theoretical advances that have led to our understanding of this simplest photo-double-ionization process, particularly with respect to multiply differential cross sections, are described.

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A continuum state of two electrons with momenta k1 and k2 can be represented as a linear combination of two-electron states with quantum numbers L, M, S and pi . Conditions are derived for which a given LMS pi state gives a vanishing contribution to the population of a state of given k1 and k2 in an arbitrary process leading to a two-electron continuum state.