Vacuum-UV absorption spectrum of a laser-produced chromium plasma: 3p-subshell photoabsorption by Cr2+ ions

The dual laser plasma photoabsorption technique has been used to measure th e time-resolved vacuum-UV photoabsorption spectrum of a chromium plasma. Re sonant photoabsorption cross sections, constructed with the aid of Hartree- Fock calculations, and weighted in accordance with the plasma temperature, have been used to produce the synthetic Cr2+ spectra The relevant plasma te mperature and ionization balance are obtained from simple analytical models for various times during the expansion phase of the plasma plume. The expe rimental spectra taken at delays of 32, 62 and 90 ns compare well with Cr2 spectra computed for corresponding predicted temperatures. It is found tha t in order to produce synthetic spectra that match experiment well, it is n ecessary to take into account absorption from many states belonging to the Cr2+ ground state configuration 3p(6)3d(4), while states from the nearest m etastable configuration 3p(6)3p(3)4s make a negligible contribution.