Competition between radiative and non-radiative decay for the doubly-excited 1s23lnl' states in O4+

Abstract

Using a B-spline based basis set, energies, radiative and autoionization rates are calculated for 1s23lnl' (n <or= 5) singlet terms in the doubly-excited Be-like oxygen ion and compared with experimental and theoretical results where available. The truncated diagonalization method is extended by including a second-order energy correction and a first-order correction to the independent channel approximation in the determination of the autoionization decay rates. The 1s2 core is taken into account by a model potential as well as by a frozen HF 1s wavefunction. To estimate the importance of radiative decay, branching ratios between radiative and non-radiative decay are determined, most of them for the first time. Radiative decay is only of importance for states with parity pi = (-1)L+1. Core effects are similar in both approaches. Compared to the isoionic 3lnl' states in C4+ a rather different and less regular behaviour of the decay properties with n is observed for 1s23lnl' in O4+ due to the presence of the 1s2 core.