Calculation of the near threshold photoabsorption for the ground and excited sodium states

Abstract

We revisit the photoabsorption from the ground state of Na, ending below and above the ionization threshold, with special emphasis on the shape of the photoionization cross section around the Cooper minimum. The present treatment, using a self-consistent central field and including core polarization effects, matches and improves over the results of other recent calculations. The photoabsorption from the excited $4s,$ $3p$, and $3d$ states is also calculated, along with the corresponding optical oscillator strengths. The results are compared with all published experimental and with the most representative of the theoretical data. The comparisons confirm the results of some of the measurements, but raise serious concerns about the validity of others. The continuing disagreement in the case of the ground state with the only one available experimental measurement, that is over 55 years old, points to the needs for new, refined, measurements.