Extreme-UV photoabsorption spectrum of a laser-produced silicon plasma: evidence for metastable Si ions

Time- and space-resolved extreme ultraviolet (XUV) photoabsorption spectra of a laser-produced silicon plasma have been recorded using a dual-laser-produced plasma technique. Under appropriate experimental conditions we have been able to measure structure due to 2p-subshell excitation from metastable quartet states of the configuration. The experimental spectrum is compared to a spectrum synthesized with computed data from the Cowan suite of atomic structure codes. Eigenvector data from the atomic structure calculations performed in LS coupling are used to assign most of the observed resonance structures and a number of the 2p-subshell ionization limits of atomic silicon are inferred from the experimental data.