Absolute Photoionization Cross Sections for Br$^{2+}$ in the 4$\it{p}\rightarrow$4$\it{d}$ and 3$\it{d}\rightarrow$4$\it{p}$ Energy Regions

Absolute single photoionization cross-section measurements are reported for Br$^{2+}$ in the 31 eV to 46 eV and 64 eV to 72 eV photon energy ranges. The first energy range includes the low-lying $^2P_{3/2,1/2}$ and $^2D_{5/2,3/2}$ metastable state thresholds and extends for 10 eV above the $^4S_{3/2}$ ground state threshold. Strong photoexcitation-autoionization resonances due to 4p$\rightarrow$$\it{n}d$ transitions are seen in the cross-section spectrum and identified based on a quantum-defect analysis of the series. The systematic behavior of the quantum defect parameter of some of the Rydberg series observed in the Br$^{2+}$ spectrum as well as in previously measured Se$^+$ spectrum, are analyzed as a function of the nuclear charge. The 64 eV to 72 eV energy range contains discrete structure that arises from 3$\it{d}\rightarrow$n$\it{p}$ excitations. The $R$-matrix photoionization cross section calculations of Cummings and O'Sullivan, PRA, 54 (1996) are compared to our absolute cross section measurements in this energy range.