Influence of core-polarisation effects on the photoionisation cross sections of the ground level and excited ns levels of neutral sodium

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Abstract
Photoionisation cross sections for the ground level and some excited ns levels (n up to 14) of neutral sodium have been computed for low photoelectron energies. Starting from a single-particle central-field model, perturbation theory is used to estimate the contribution of potential corrections and core-polarisation effects. For the ground level in the agreement between our results and previous data (experimental and theoretical) is greatly improved by the inclusion of these corrections. The evolution of cross sections and core-polarisation effects along the ns Rydberg series is investigated; core-polarisation effects have larger relative magnitude for the ground level and the low excited levels than for the high excited ones.