Intercombination lines in highly charged Al- and Si-like ions

Delayed spectroscopy techniques have been used to study the isoelectronic development for Al-like and Si-like intercombination line wavelengths. The ions studied range from Kr to Nb. The trend established for the quantity (E-obs - E-calc)/zeta, (E being the transition energy and zeta the effective charge), shows that the available calculated data are not useful in identifying such intercombination lines for high Z ions. In the case of the Si-like intercombination lines the difference in wavelength between experiment and calculation is around 4 Angstrom for Nb27+ and this difference increases for higher Z ions. The line identifications were aided by recording spectra for different charge state distributions of the ions after the exciter foil. The experiments were done using ion beams from the RILAC accelerator at RIKEN.