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 ²Sᵉ and ²Pᵒ 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 ²S ion state due to initial-state correlations. The first momentum profiles for excited states belonging to the ²Pᵒ and ²Dᵉ 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 (¹D) excitations in describing electron correlations in both the initial Ar ground state and in the final ionic states.