Excitation Energies, Oscillator Strengths and Lifetimes in Ca IX

Abstract

We have calculated the excitation energies for the lowest 46 LS and 86 fine-structure levels as well as oscillator strengths and radiative decay rates for transitions among the (1s22s22p6)3s2(1S), 3s3p(1,3Po), 3s3d(1,3D), 3s4s(1,3S), 3s4p(1,3Po), 3s4d(1,3D), 3s4f(1,3Fo), 3p2(1S, 3P, 1D), 3p3d(1,3Po, 1,3Do, 1,3Fo), 3p4s(1,3Po), 3p4p(1,3S, 1,3P, 1,3D), 3p4d(1,3Po, 1,3Do, 1,3Fo), 3p4f(1,3D, 1,3F, 1,3G) and 3d2(1S, 3P, 1D, 3F, 1G) states in Ca IX. These states are represented by extensive configuration-interaction (CI) wavefunctions obtained with the CIV3 computer code of Hibbert. From our transition probabilities we have also calculated the radiative lifetimes of singlet and triplet states of Ca IX. Our results are compared with other available theoretical calculations and experimental data. To assess the importance of relativistic effects on our calculated values, we have also carried out calculations in the intermediate-coupling scheme. These effects are incorporated through the Breit-Pauli approximation via spin-orbit, spin-other-orbit, spin-spin, Darwin and mass correction terms. In order to keep our calculated energy splittings as close as possible to the experimental values, we have made small adjustments to the diagonal elements of the Hamiltonian matrices. The energy splittings of 87 fine-structure levels, the oscillator strengths and transition probabilities for some strong dipole-allowed and intercombination transitions and the lifetimes of some fine-structure levels are presented and compared with available experimental and other theoretical values. Our calculated lifetimes of the relatively long-lived 3p3d(3FJ) levels show remarkable improvement over the theoretical values of Fawcett, compared to the experimental results of Trabert et al. Also, our lifetime for the 3p2(1D2) level calculated in intermediate-coupling scheme, while differing significantly from our LS value, shows good agreement with the experimental value and thus confirms the need to include relativistic effects in calculations. In this calculation we also predict new data for several levels where no other theoretical and experimental results are available.