Regularities in calculated photoionization cross sections for the halogens

The total photoionization cross sections of F, Cl, Br, and I are calculated near the ns²{np}⁴$ thresholds. They show excellent agreement with experiment for all of the halogens except I whose cross section is only in fair agreement with experiment. At the $¹$S threshold of Cl our results agree with experiment and with the highest of the previous calculations. These results suggest that atomic theory is now capable of reproducing the dynamics of all the open-p-shell atoms with Z54, at energies near the lower ionization thresholds. We identify a type of mixing which goes beyond the usual recoupling frame transformation and is not present in alkaline-earth atoms, nor in rare-gas atoms.