Metastable state contributions to the measured 3p photoabsorption spectrumof Cr+ ions in a laser-produced plasma

Recently, the spectrum of singly ionized chromium has come under theoretica l scrutiny by Dolmatov (1996 J. Phys. Br At. Mel. Opt. Phys. 29 L673) and a lso by Donnelly et al (1997 J. Phys. B: At. Mel. Opt. Phys. 30 L285). Both of these theoretical investigations, employing the spin-polarized RPAE (SPR PAE) and R-matrix techniques, respectively, concerned the 3p photoabsorptio n cross section from the 3d(5) S-6(5/2) ground state of Cr+. The two calcul ations are consistent with each other and agree with the previously reporte d experimental data for the 3p --> 4s resonances and the onset of the 3p -- > 3d giant resonance (Costello 1991 Phys. Rev. A 43 1441). However, beyond the peak of the giant resonance, both calculations result in cross sections which differ considerably from the experimental data. From further dual-la ser plasma experiments carried out under different spatio-temporal conditio ns and atomic structure calculations on metastable states this discrepancy can be ascribed to the presence of metastable excited singly ionized chromi um within the plasma.