EUV photoabsorption of laser produced tellurium plasmas: Te I-Te IV

The photoabsorption spectra of Te I through to Te IV have been recorded in the extreme ultraviolet (EUV) region using the dual laser plasma (DLP) technique. Photoexcitation from the 4d subshell is the dominant process in the 50 to 130 eV region. Above the 4d ionization thresholds the spectra were found to be dominated by a 4d →εf shape resonance which peaks at 88 eV in each case, indicating that complete 4f 'collapse' has not occurred in stages up to and including Te³⁺. A transfer of oscillator strength from the resonance to the pseudo-discrete 4d →nf (n ≥ 4) transitions with increasing ionization is evident from Te²⁺ onwards with the transition being the strongest feature in the Te IV spectrum. Time-dependent local density approximation (TDLDA) calculations successfully account for the shape resonance while Hartree-Fock with configuration interaction calculations permit identification of the discrete features.