Configuration interaction between doubly and singly excited bound states

We present the results of a theoretical investigation on the configuration interaction between doubly excited ($n_1$$l_1$,$n_2$$l_2$${)}^1$,3L and singly excited (3snl${)}^1$,3L bound states below the first ionization threshold of atomic ions which are isoelectronic to the magnesium atom. The effect of configuration interaction is studied in terms of (i) the term values correction and (ii) the change in oscillator strengths for transitions involving the neighboring singly excited states due to the presence of an individual doubly excited perturber. The range and strength of each bound doubly excited state in Al ii and Si iii ${}_{}{}^1{}_{}{}^{}$,3S${\mathrm{-}}^1$,3F series are examined in detail.