ANALYSIS OF CORRELATION-EFFECTS IN AUTOIONIZING DOUBLY-EXCITED STATESOF BARIUM USING COULOMB GREENS-FUNCTION

Though one would expect that large-angular momentum doubly excited sta tes exhibit weak electronic correlations, it is shown in this paper th at a first-order perturbation theory ignoring such correlations may co mpletely fail in predicting correct autoionization probabilities: quad rupolar transitions are poorly described by lowest-order perturbation theory, except for very large angular momenta. Inclusion of second-ord er dipole-dipole term considerably improves the accuracy of the method . This effect is computed using Coulomb Green's function in its analyt ical form, probably applied here for the first time to autoionization processes. Examples are given in barium for 5d(j) 5g [k] states (j = 3 /2, 5/2) and for 5d(5/2) nl [k] states with l > 4.