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 bee n 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 avenge energy of configuration multiconfiguration Hartree-F ock calculations and Rydberg series expansion. The 3p --> nd series in Sc rv is seen to be considerably weaker for n > 3 than for adjacent i ons. The random-phase approximation with exchange calculations confirm this behaviour and show that it originates from a change in sign of t he 3p --> nd dipole matrix element between n = 4 and n = 5 in this spe ctrum.