Trends in 4d-subshell photoabsorption along the iodine isonuclear sequence: I, I+, and I2+

The 4d absorption spectra of I, I+, and I2+ have been observed in the 45-300-eV region using the dual laser-produced plasma technique. At lower energies each spectrum is dominated by intense 4d-->5p transitions, which are identified with the aid of multiconfiguration Hartree-Fock calculations. The excited states decay by direct autoionization involving 5s or 5p electrons and rates for the different processes and resulting linewidths were calculated and compared, where possible, with experiment. In the case of neutral iodine 4d-->6p transitions are also observed in the region close to the D-2(5/2), threshold. The dominant feature in each spectrum, however, arises from 4d-f excitation, which evolves from a 4d-epsilon f shape resonance in neutral iodine to a feature containing discrete 4d-->nf transitions in I2+.