Level energies and lifetimes in the 3p4 3d configuration of chlorine-like ions

Abstract

Large-scale multiconfiguration Dirac-Fock wavefunctions have been used to study excitation energies and lifetimes of the 3s2 3p4 3d configuration in the chlorine isoelectronic sequence. We present an ab-initio calculation of all dipole allowed transitions from 3s2 3p4 3d to the 3s2 3p5 (J = 1/2, 3/2) ground state levels for 6 ions in the atomic range 18 ≤ Z ≤ 41. To generate the wavefunctions we used the active-space method outside a closed 1s2 2s2 2p6 core. Our study incorporates the major correlation effects by including all virtual single, double and triple excitations into the 3l subshells as well as all singles and doubles into 4l. Excitations into the 4l and higher subshells do not contribute so much to the transition energies, but they clearly affect the transition probabilities and lifetimes. Additionally, the rearrangement of the electron density during the spontaneous emission is taken into account by a separate optimization of the wavefunctions in the 3p4 3d and 3p5 configurations. This often reduces the deviations between the lifetimes in different gauge forms, in particular at the neutral end of the isoelectronic sequence. Comparison is made with previous calculations and available experimental data. We conclude that the accuracy of the presented excitation energies (apart from Ar II) has been improved to about 5000 cm−1 for higher charged ions, i.e. by about a factor of 2 or so with respect to recent computations.