COMPETITION BETWEEN RADIATIVE AND NONRADIATIVE DECAY FOR THE DOUBLY-EXCITED 1S(2)3LNL'STATES IN O-4+

Using a B-spline based basis set, energies, radiative and autoionizati on rates are calculated for 1s(2)3lnl' (n less-than-or-equal-to 5) sin glet terms in the doubly-excited Be-like oxygen ion and compared with experimental and theoretical results where available. The truncated di agonalization method is extended by including a second-order energy co rrection and a first-order correction to the independent channel appro ximation in the determination of the autoionization decay rates. The 1 s2 core is taken into account by a model potential as well as by a fro zen HF Is wavefunction. To estimate the importance of radiative decay, branching ratios between radiative and non-radiative decay are determ ined, most of them for the first time. It is found that radiative deca y is only of importance for states with parity pi = (-1)L+1. Core effe cts are similar in both approaches. Compared to the isoionic 3lnl' sta tes in C4+ a rather different and less regular behaviour of the decay properties with n is observed for 1s(2)3lnl' in O4+ due to the presenc e of the 1s2 core.