We have measured the photoabsorption spectra of the Kr-like ions ${\mathrm{Rb}}^{+}$ and ${\mathrm{Sr}}^{2+}$ at photon energies corresponding to the excitation of $4s-\mathrm{np}$ resonances using, the dual laser plasma photoabsorption technique. Dramatic changes in the line profiles, with increasing ionization and also proceeding along the Rydberg series of each ion, are observed and explained by the trends in $4s$-transition amplitudes computed within a framework of configuration-interaction Pauli-Fock calculations. Total photoionization cross sections show very good agreement with relative absorption data extracted from the measured spectra.

• Received 24 October 2002

DOI:https://doi.org/10.1103/PhysRevA.67.042707