The evolution of 4d photoabsorption in Sb with increasing ionization

The photoabsorption spectra of Sb+, Sb2+,Sb3+ and Sb4+ have been obtained i n the XUV spectral region with the dual laser-produced plasma (DLP) techniq ue. Photoexcitation from the 4d subshell is the dominant process in the 30- 100 eV energy region. In Sb+, for photon energies between 30 and 50 eV, dis crete structure corresponding to 4d --> np, n(1)f (n greater than or equal to 5, n(1) greater than or equal to 4) transitions is obtained, while above 50 eV the spectrum is dominated by an intense 4d --> epsilon f resonance. Apart from the 4d --> 5p transitions the features are very weak. The 4d --> epsilon f resonance is still observed in Sb2+ as the dominant feature in t he spectrum, but in Sb3+ and Sb4+ there is significant transfer of oscillat or strength from the continuum to the discrete spectra, in particular to th e 4d --> nf transitions. This behaviour mirrors the effects of contraction of the 4f wavefunction, which is seen to be more gradual here than in eleme nts with Z > 54. Multiconfiguration Hartree-Fock and time-dependent local d ensity approximation calculations successfully reproduce this behaviour.