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 $^{1}\mathrm{S}$ 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.