Satellite structure in the argon valence shell by electron-momentum spectroscopy

Momentum distributions and spectroscopic factors are obtained in a high-resolution study of argon at 500, 1000, and 1500 eV by electron-momentum spectroscopy. The shapes and relative magnitudes of the 1500-eV cross sections are in excellent agreement with the results of a distorted-wave impulse approximation calculation. The final states belonging to the ${}_{}{}^2{}_{}{}^{}\mathrm{S}_{}^{\mathrm{e}}{}_{}{}^{}$ and ${}_{}{}^2{}_{}{}^{}\mathrm{P}_{}^{\mathrm{o}}{}_{}{}^{}$ manifolds are identified and their spectroscopic factors (pole strengths) are obtained. These are found to be independent of energy and momentum in the range 0.1–1.9 a.u. within experimental error, although some momentum dependence is observed for the spectroscopic factor leading to the 4s ${}_{}{}^2{}_{}{}^{}S$ ion state due to initial-state correlations. The first momentum profiles for excited states belonging to the ${}_{}{}^2{}_{}{}^{}\mathrm{P}_{}^{\mathrm{o}}{}_{}{}^{}$ and ${}_{}{}^2{}_{}{}^{}\mathrm{D}_{}^{\mathrm{e}}{}_{}{}^{}$ manifolds are obtained. The latter are entirely due to initial-state correlations. Comparison is made with several many-body calculations. The data show the importance of core quadrupole ${(}^1$D) excitations in describing electron correlations in both the initial Ar ground state and in the final ionic states.