Analysis of core-excited n = 3 configurations in S VI, Cl VII, Ar VIII and Ti XII

By means of the beam-foil method, 74 new lines have been identified as combinations between the core-excited 2p⁵ 3s3p, 3s3d and 3p² configurations in Na-like sulphur, chlorine, argon and titanium. Relative energies have been determined for most of the quartet levels in S, Cl and Ar with an internal uncertainty of less than 25 cm⁻¹. We also report the first observation in the isoelectronic sequence of Δn = 0, n = 3 transitions from the quasi-metastable 2p⁵ 3p²(³P) ²D_5/2 level. The identifications are supported by isoelectronic studies and comparisons with theoretical results obtained in superposition-of-configuration calculations including continuum channels.