Excitation energies, E1, M1, and E2 transition rates, and lifetimes in Ca⁺, Sr⁺, Cd⁺, Ba⁺, and Hg⁺ ¹This article is part of a Special Issue on the 10th International Colloquium on Atomic Spectra and Oscillator Strengths for Astrophysical and Laboratory Plasmas.

Excitation energies of ns 1/2 , np j , and nd j states in Cd + (n = 5), Hg + (n = 5) and ns 1/2 , np j , and (n – 1)d j states in Ca + (n = 4), Sr + (n = 5), and Ba + (n = 6) are evaluated using the linearized coupled-cluster (all-order) method. Reduced matrix elements, oscillator strengths, and transition rates are determined for the ns–np j –nd j (or ns–np j –(n – 1)d j ) possible electric dipole transitions in Ca + , Sr + , Ba + , Cd + , and Hg + . Electric quadrupole matrix elements are evaluated to obtain ns 1/2 –(n – 1)d j transition rates in Ca + (n = 5), Sr + (n = 5), and Ba + (n = 6). The matrix elements are calculated using both relativistic many-body perturbation theory, complete through third order, and the relativistic all-order method restricted to single and double (SD) excitations. The SD lifetime results for the np and nd states in Ca + , Sr + , Ba + , Cd + , and Hg + , are compared with the latest available experimental measurements. The contribution of the magnetic dipole nd 3/2 –nd 5/2 transition to the lifetimes of the lowest nd 5/2 level ln Ca + , Sr + , and Ba + ions is discussed. These calculations provide a theoretical benchmark for comparison with experiment and theory as well as data needed for various applications.