Photoionization cross section for the4ssubshell of Zn I

We present a calculation of the photoionization cross section for the $4s$ subshell of neutral zinc using many-body perturbation theory. The cross section is strongly affected by correlations among $4s$ and $3d$ electrons. Resonances due to the $3d^{9}4s^2\mathrm{np}$ configurations dominate the cross section and are split by the spin-orbit interaction. We have also included interactions between resonances. Correlations reduce the Hartree-Fock cross section by an order of magnitude near threshold. Our results are in qualitative agreement with the experimental data of Marr and Austin.