Photoionization from Outer Atomic Subshells. A Model Study

Abstract

Calculations of photoionization cross sections are reported which emphasize the spectral range (from threshold to \ensuremath{\sim}150 eV above it) where the bulk of the optical oscillator strength is distributed and where the cross sections are large but experimental evidence is scarce. We have used as a model the light absorption by a single electron moving in a potential similar to the Hartree-Fock potential appropriate to the outer subshell of each atom. Data are reported for the rare gases He, Ne, Ar, and Kr, for Na, and for the closed-shell ions ${\mathrm{Cu}}^{+}$ and ${\mathrm{Ag}}^{+}$. Sum rules are used to analyze the oscillator strength spectral distribution and to attempt extrapolations to still higher energies. The results suggest a classification of atomic subshells into two types with fundamentally different spectral distributions of oscillator strength. One type consists of the subshells $1s$, $2p$, $3d$, $4f$, with nodeless radial wave functions, the other type includes all remaining subshells. The present calculations are regarded as a first approximation to be improved upon by taking into account configuration interaction.