The electronic rearrangement resulting from the ␤ decay of 6 He has been calculated in the framework of the sudden approximation using a numerical B-spline basis set approach. We have calculated the excitation probabilities to the final discrete states of 6 Li ϩ ͑including to the doubly excited autoionizing states͒ as well as the total probabilities for single and double ionization. The correct treatment of electronic correlation in the framework of the sudden approximation is shown to modify the P K value ͑the probability that an atomic K vacancy is created͒ by more than 2%.

The electronic redistribution of an ion or atom induced by a sudden recoil of the nucleus occurring during the emission or capture of a neutral particle is theoretically investigated. For one-electron systems, analytical expressions are derived for the electronic transition probabilities to bound and continuum states. The quality of a B-spline basis set approach is evaluated from a detailed comparison with the analytical results. This numerical approach is then used to study the dynamics of two-electron systems (neutral He and Ne 8+ ) using correlated wavefunctions for both the target and daughter ions. The total transition probabilities to discrete states, autoionizing states and direct single-and double-ionization probabilities are calculated from the pseudospectra. Sum rules for transition probabilities involving an initial bound state and a complete final series are discussed.