Polarizabilities of the Mg^+ and Si³⁺ ions

A polarization analysis of the fine-structure intervals for the $n = 17$ Rydberg states of Mg and the $n = 29$ states of Si$^{2+}$ is performed. The coefficients of all terms in the polarization expansion up to $r^{-8}$ were computed using a semi-empirical single electron analysis combined with the relativistic all-order single-double method (MBPT-SD) which includes all single-double excitations from the Dirac-Fock wave functions to all orders of perturbation theory. The revised analysis yields dipole polarizabilities of $\alpha_1 = 35.04(3)$ a.u. for Mg$^+$ and $\alpha_1 = 7.433(25)$ a.u. for Si$^{3+}$, values only marginally larger than those obtained in a previous analysis (E. L. Snow and S. R. Lundeen (2007) Phys. Rev. A {\bf 75} 062512, {\em ibid} (2008) {\bf 77} 052501). The polarizabilities are used to make estimates of the multiplet strength for the resonant transition for both ions. The revised analysis did see significant changes in the slopes of the polarization plots. The dipole polarizabilities from the MBPT-SD calculation, namely 35.05(12) a.u. and 7.419(16) a.u., are within 0.3% of the revised experimental values.