Lifetimes and Oscillator Strengths for Ultraviolet Transitions in Ge II

Better understanding of the atomic structure for atomic ions requires experimental measurements for lifetimes and oscillator strengths which also serve as a test for theoretical calculations. Furthermore, interpreting astronomical observations of atomic ions requires knowledge of their oscillator strengths and transition probabilities. We present the results of lifetime measurements with beam-foil techniques performed with the Toledo Heavy-Ion Accelerator on levels of interest in Ge~{\footnotesize II} producing transitions to the ground term at 1237.1 {\AA} and 1261.9 {\AA} ($4s^{2}4d$ $^{2}D_{3/2}$ and $4s^{2}4d$ $^{2}D_{5/2}$, respectively). Oscillator strengths are derived from the lifetimes, and our experimental results are compared with our MCDHF\footnote[2] {P. J{\"{o}}nsson et al., The Computational Atomic Structure Group (2014)} calculations using the development version of the GRASP2K package\footnote[3] {P. J{\"{o}}nsson et al., Comput. Phys. Commun. 184, 2197 (2013)} as well as the latest calculations done by others. We also provide an overall comparison of our studies on the $ns^{2}nd$ $^{2}D$ and $nsnp^{2}$ $^{2}D$ terms in three elements of group~{\footnotesize IV} of the periodic table, namely Pb~{\footnotesize II}, Sn~{\footnotesize II} and Ge~{\footnotesize II}.