A Critical Test of Many-Body Theory: The Photoionization Cross Section of Cl as an Example of an Open-Shell Atom

Abstract
The present work reports the first absolute photoionization cross-section measurements for the open-shell atom chlorine. Measurements were made from the S1 ionization threshold at 16.4 eV to 75 eV. Agreement with several calculations is good at the higher photon energies. We have observed a Cooper minimum at about 44 eV as predicted by theory. However, near threshold the various calculations differ considerably with each other and with the present results.