EXTREME-ULTRAVIOLET ABSORPTION-SPECTRUM OF GA+

Time-resolved photoabsorption spectra of gallium plasmas have been pho tographed in the 50-450-angstrom region using the dual-laser-produced- plasma technique. The absorbing plasmas were produced by focusing the output of a Q-switched ruby laser onto slab targets while the backgrou nd continuum was produced by focusing the output of a Nd:YAG oscillato r-amplifier system (where Nd:YAG denotes neodymium-doped yttrium-alumi num-garnet) onto a samarium or hafnium target. At 130-ns delay between the two pulses the spectrum recorded was due almost exclusively to Ga +. We have observed transitions due to both 3d and 3p excitation. In t he former case we identified 3d(10)4s2-3d(9)4s2nf and 3d(9)4s2np serie s converging on the 2D3/2 and 2D5/2 limits of Ga2+. In the 3p case no strong transitions were observed because of line broadening by super-C oster-Kronig decay of the 3p hole. The identifications were made by co mparison with the predictions of Hartree-Fock and Dirac-Fock atomic-st ructure codes. Many-body calculations were also performed which proved invaluable in estimating the effects of different decay processes. Th e theoretical predictions are compared with the experimental data.