3dabsorption spectra of Sr i through Sr iv

The extreme ultraviolet photoabsorption spectra of neutral to three-times-ionized strontium have been recorded in a comprehensive series of experiments with the dual laser-produced plasma technique. Striking differences were found in the spectra, which can be attributed to the transfer of oscillator strength from 3d{→}np to 3d{→}nf transitions at Sr²⁺ due to nf wave-function contraction. In Sr and Sr⁺, 3d{→}5p transitions dominate; in Sr²⁺, 3d{→}nf transitions are most intense, while in Sr³⁺ the 4p subshell opens and 3d{→}4p transitions are the strongest features. Partial cross sections for 3d{→}{ε}f and 3d{→}{ε}p photoionization were calculated and compared with experiment.