Oscillator strengths of allowed and intercombination lines in Si II using non-orthogonal wavefunctions

Abstract

The importance of valence–shell, core–valence and core–core correlation and interactions between the members of 3s2nd 2D Rydberg series and between the Rydberg series and 3s3p22D perturber state in singly ionized silicon has been examined using term-dependent non-orthogonal orbitals in the multiconfiguration Hartree–Fock approach. Large sets of spectroscopic and correlation non-orthogonal functions have been chosen to adequately describe the term dependence of wavefunctions, various correlation corrections and strong interactions in Rydberg series. The relativistic corrections are included through the one-body mass correction, Darwin and spin–orbit operators and two-body spin–other-orbit operator in the Breit–Pauli Hamiltonian. Extensive configuration-interaction wavefunctions have been used in the representation of Si II levels to calculate oscillator strengths and transition probabilities. The accuracy of present oscillator strengths is evaluated by the agreement between the length and velocity formulations combined with the agreement between the calculated and measured transition energies. The present results have been compared with previous calculations, experimental measurements and astronomical observations.