R-matrix analysis of the 6d²and 7p²autoionizing resonances of barium

A method is presented for adapting the streamlined eigenchannel R-matrix approach to the analysis of 6d 2 and 7p 2 autoionizing resonances of Ba. The doubly excited states are assumed to be confined within the reaction volume. R-matrix calculations are carried in LS coupling for the 1 S, 3 P, 1 D, 3 F and 1 G symmetries and in jj coupling for J=0 e to J=4 e . For each symmetry, an R-matrix restricted to open channels is constructed using a variational basis allowing the identification of the doubly excited states. From the R-matrix the authors deduce a scattering S-matrix which is expressed as the sum of resonant and non-resonant parts, i.e. in a form suited to resonance analysis. The positions and autoionization widths of 6d 2 and 7p 2 levels are predicted from the energy dependence of the density of states matrix, equivalent to the time-delay matrix. The approach is connected with other theories, in particular with Fano's configuration interaction method which treats bound levels embedded in continua.