Multielectronic excitations near theKedge of argon

High-resolution x-ray photoabsorption measurements on Ar near its K edge are reported. A number of new two-electron KM features were detected. The three-electron ${\mathit{KM}}^2$ and the two-electron KL spectra were measured for the first time. The three-electron ${\mathit{KM}}^2$ and the two-electron KL spectra were measured. The previously unresolved three-electron ${\mathit{KM}}^2$ and the two-electron KL spectra were clearly resolved in this study. Identification of spectral features is discussed based on our Hartree-Fock and published Dirac-Fock [Dyall, J. Phys. B 16, 3137 (1983); Dyall and LaVilla, Phys. Rev. A 34, 5123 (1986)] energy-level calculations.