Trends in 3p photoabsorption in the Ar I isoelectronic sequence: spectra of Sc IV and Ti V

The 3p → ns, nd Rydberg series of argon-like Sc IV and Ti V have been observed using the dual-laser-produced plasma method. Lines arising from transitions up to n=8 have been identified in the Ti V spectrum using the average energy of configuration multiconfiguration Hartree - Fock calculations and Rydberg series expansion. The 3p→nd series in Sc IV is seen to be considerably weaker for n>3 than for adjacent ions. The random-phase approximation with exchange calculations confirm this behaviour and show that it originates from a change in sign of the 3p→nd dipole matrix element between n=4 and n=5 in this spectrum. (author). Letter-to-the-editor