Photoionization ofFe7+from the ground and metastable states

Abstract

The $B$-spline Breit-Pauli $R$-matrix method is used to investigate the photoionization of ${\mathrm{Fe}}^{7+}$ from the ground and metastable states in the energy region from ionization thresholds to 172 eV. The present calculations were designed to resolve the large discrepancies between recent measurements and available theoretical results. The multiconfiguration Hartree-Fock method in connection with $B$-spline expansions is employed for an accurate representation of the initial- and final-state wave functions. The close-coupling expansion includes 99 fine-structure levels of the residual ${\mathrm{Fe}}^{8+}$ ion in the energy region up to $3{s}^{2}3{p}^{5}4s$ states. It includes levels of the $3{s}^{2}3{p}^{6},3{s}^{2}3{p}^{5}3d,3{s}^{2}3{p}^{5}4s$, and $3s3{p}^{6}3d$ configurations and some levels of the $3{s}^{2}3{p}^{4}3{d}^{2}$ configuration which lie in the energy region under investigation. The present photoionization cross sections in the length and velocity formulations exhibit excellent agreement. The present photoionization cross sections agree well with the Breit-Pauli $R$-matrix calculation by Sossah et al. and the TOPbase data in the magnitude of the background nonresonant cross sections but show somewhat richer resonance structures, which qualitatively agree with the measurements. The calculated cross sections, however, are several times lower than the measured cross sections, depending upon the photon energy. The cross sections for photoionization of metastable states were found to have approximately the same magnitude as the cross sections for photoionization of the ground state, thereby the presence of metastable states in the ion beam may not be the reason for the enhancement of the measured cross sections.