The M-shell photoabsorption spectrum of Ge²⁺

The dual laser produced plasma (DLP) technique, has been used to study the EUV absorption spectra of germanium plasmas in the 50-400 AA region. The absorbing plasmas were produced by focusing the output of a Q-switched ruby laser onto a germanium target while the background continuum was produced by focusing the output of a Nd:YAG oscillator/amplifier system onto a samarium target. At a time delay of 50 ns and an absorbing plasma column length of 2 mm the spectrum recorded was predominantly due to Ge2+. We have investigated 3d and 3p sub-valence transitions. In the former, 3d104s2 to 3d94s2nf and 3d94s2np series converging on the 2D5/2 and 2D3/2 limits of Ge3+ were identified by isoelectronic comparison and Hartree-Fock calculations. In the 3p case no strong line transitions were observed which was shown by many body calculations to result from line broadening caused primarily by super Coster-Kronig decay of the 3p hole.