Theory of the neon1scorrelation-peak intensities

Abstract

The correlation-state spectrum accompanying $1s$ photoemission in atomic neon was calculated by several methods, using the sudden approximation and focusing on states that are approximately described by single-electron excitation of the form $2p\ensuremath{\rightarrow}np$. All the calculations gave satisfactory energy values, but the predicted intensities differed widely. Multiconfiguration Hartree-Fock (MCHF) orbitals and orthogonalized MCHF orbitals gave intensities in poor agreement with experiment. A final-state configuration-interaction calculation gave accurate energies for seven $2p\ensuremath{\rightarrow}np$ correlation states, but when combined with a single-determinant initial state, yielded intensities low by about a factor of 2. Initial-state configuration interaction (ISCI), including double-electron excitation of the form $2{p}^{6}\ensuremath{\rightarrow}2{p}^{4}n{p}^{2}$, etc., brought the intensities of the $2{p}^{5}\mathrm{np}$-type states into agreement with experiment. It was thus shown that ISCI is of equal importance to final-state CI in determining correlation-peak intensities. Correlation-state (or shakeup) spectra therefore contain unique information about electron correlation in the ground state.