A beam-foil study of Ni XIX and Cu XX and a theoretical survey of 2p53l configurations from Ar IX to Cu XX

The spectra of the neon-like ions Ni XIX and Cu XX have been studied by beam-foil techniques. About 30 lines have been used in each spectrum to derive the energy levels of the 2p 5 3l configurations. The identifications are supported by systematic theoretical studies using the Slater-Condon parametric method with isoelectronic constraints in the fitting process, and the ab initio relativistic parametric potential method. Some earlier identifications have been revised in the sequence Ar IX-Cu XX.