The evolution of 4d photoabsorption in Sb with increasing ionization

The photoabsorption spectra of Sb⁺ , Sb²⁺ , Sb³⁺and Sb⁴⁺have been obtained in the XUV spectral region with the dual laser-produced plasma (DLP) technique. 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, discrete structure corresponding to 4dn p, n¹ f (n 5,n¹ 4) transitions is obtained, while above 50 eV the spectrum is dominated by an intense 4d f resonance. Apart from the 4d 5p transitions the features are very weak. The 4d f resonance is still observed in Sb²⁺as the dominant feature in the spectrum, but in Sb³⁺and Sb⁴⁺there is significant transfer of oscillator strength from the continuum to the discrete spectra, in particular to the 4dn f transitions. This behaviour mirrors the effects of contraction of the 4f wavefunction, which is seen to be more gradual here than in elements with Z >54. Multiconfiguration Hartree-Fock and time-dependent local density approximation calculations successfully reproduce this behaviour.