Photoionisation cross section of the ground state of neutral sodium

The photoionisation cross section of the ground state of neutral sodium is calculated with the close-coupling method. Polarisation of the 2p 6 core by the valence electron is included in an ab initio manner by the use of polarised pseudo-states. The contribution to the radiative dipole matrix element due to core polarisation is shown to increase the cross section significantly at energies above the minimum. Good agreement is found with the experimental results if the latter are scaled by a factor of about 0.7, which suggests that the experimental curve should be renormalised. Oscillator strengths are also presented for 3s-np transitions are are compared with other theoretical results.