Comparison of final state approximations in the calculation of total and differential photoemission cross sections of neon

Differential photoemission cross sections for the 1s, 2s, and 2p shells of neon were calculated by several different approximations for photon energies up to 2000 eV. Specifically, plane wave (PW), orthogonalized plane wave (OPW), and Hartree–Fock functions (with and without consideration of relaxation in the final ionic state) were used to compute transition matrix elements in both velocity and length approximations. Plane wave and orthogonalized plane wave continuum functions were found to have very limited applicability to cross section calculations, with both approximations giving spurious local minima and incorrect angular distributions. The reasons for these failures were analyzed, and limits were set on the n, l, and z values for which the PW model yields qualitatively correct total cross sections. Calculations using Hartree–Fock continuum functions agree very well with experiment, emphasizing the necessity of considering atomic potentials explicitly in photoemission processes. Further, the effects of relaxation in the final bound system were investigated. They were small for valence electrons and only slightly more important for Ne 1s core electrons. Applications of these findings to photoemission from molecules and absorbates are discussed briefly.