Quantifying the Asymmetry of Giant Resonances in Sc$^{3+}$ Photorecombination and Sc$^{2+}$ Photoionization*

We report on strong interference effects for the asymmetric, broad, and highly-correlated $3p^5 3d^2({}^{2}\hspace*{-.5mm}F^{{\rm o}}_{J})$ resonances in the photorecombination of ${\rm Sc}^{3+}$. Using a perturbative multiconfiguration Breit-Pauli approach, we present theoretical photorecombination cross sections that compare favorably with the Test Storage Ring measurements of Schippers~{\em et al.}~[1]. In order to reproduce the observed asymmetric resonance profiles, it was necessary to include resonance-continuum and $3p^5 3d^2$-$3p^5 3d4s$ resonance-resonance interference to the next-highest order. By using the principle of detailed balance for the same resonance region, we also present ${\rm Sc}^{2+}$ photoionization cross sections that agree with the Advance Light Source measurements of Schippers~{\em et al.}~[2]. This higher-order perturbative method yields analytical expressions for the Fano asymmetry parameters $q$ in terms of computed radiative and autoionization transition amplitudes. \newline [1] S. Schippers, et al., Phys. Rev. A {\bf 65}, 042723 (2002). \newline [2] S. Schippers, et al., Phys. Rev. A {\bf 67}, 032702 (2003).