Absolute single photoionization cross section measurements of isoelectronic Br$^{\mathrm{3+}}$ and Rb$^{\mathrm{5+}}$ ions

Absolute single photoionization cross-section measurements of Br$^{\mathrm{3+}}$ and Rb$^{\mathrm{5+}}$ ions were performed using synchrotron radiation and the photo-ion, merged-beams technique at the Advanced Light Source at Lawrence Berkeley National Laboratory. Measurements of Br$^{\mathrm{3+}}$ were performed at a photon energy resolution of 21 meV $+$/- 3 meV from 44.79 -- 59.54 eV spanning the $^{\mathrm{3}}$P$_{\mathrm{0\thinspace }}$ground state and $^{\mathrm{3}}$P$_{\mathrm{1,2}}$ and $^{\mathrm{1}}$D$_{\mathrm{2\thinspace }}$metastable state ionization thresholds. Analysis of the measured spectrum produced a new empirical determination of the ionization potential of Br$^{\mathrm{3+}}$ of 46.977 $+$/- 0.050 eV, which is 805 meV lower than the most recently published value. Measurements of Rb$^{\mathrm{5+}}$ were made at a nominal photon energy resolution of 25.0 meV from 76.62 to 100.07 eV spanning the $^{\mathrm{3}}$P$_{\mathrm{0\thinspace }}$ground state and $^{\mathrm{3}}$P$_{\mathrm{1,2}}$, $^{\mathrm{1}}$D$_{\mathrm{2\thinspace }}$and $^{\mathrm{1}}$S$_{\mathrm{0\thinspace }}$metastable state ionization thresholds. Autoioniziation resonance series idmtifications and quantum defect behavior are compared between the systems and the results of Br$^{\mathrm{3+}}$ are compared to theory.