Relativistic many-body calculations of excitation energies, oscillator strengths, transition rates, and lifetimes in samariumlike ions

Abstract

The unique atomic properties of samariumlike ions, not yet measured experimentally, are theoretically predicted and studied in this paper. Excitation energies, oscillator strengths, transition probabilities, and lifetimes are calculated for $(5{s}^{2}+5{p}^{2}+5{d}^{2}+5s5d+5s5g+5p5f)$--$(5s5p+5s5f+5p5d+5p5g)$ electric dipole transitions in Sm-like ions with nuclear charge $Z$ ranging from 74 to 100. Relativistic many-body perturbation theory (RMBPT), including the Breit interaction, is used to evaluate retarded $E1$ matrix elements in length and velocity forms. The calculations start from a $1{s}^{2}2{s}^{2}2{p}^{6}3{s}^{2}3{p}^{6}3{d}^{10}4{s}^{2}4{p}^{6}4{d}^{10}4{f}^{14}$ Dirac-Fock potential. First-order perturbation theory is used to obtain intermediate coupling coefficients, and the second-order RMBPT is used to determine the matrix elements. The contributions from negative-energy states are included in the second-order $E1$ matrix elements to achieve agreement between length-form and velocity-form amplitudes. The resulting transition energies and transition probabilities, and lifetimes for Sm-like W${}^{12+}$ are compared with results obtained by the relativistic Hartree-Fock approximation (cowan code) to estimate contributions of the $4f$-core-excited states. Trends of excitation energies and oscillator strengths as the function of nuclear charge $Z$ are shown graphically for selected states and transitions. This work provides a number of yet unmeasured atomic properties of these samariumlike ions for various applications and as a benchmark for testing theory.