R-MATRIX ANALYSIS OF THE 6D(2) AND 7P(2) AUTOIONIZING RESONANCES OF BARIUM

A method is presented for adapting the streamlined eigenchannel R-matr ix approach to the analysis of 6d2 and 7p2 autoionizing resonances of Ba. The doubly excited states are assumed to be confined within the re action volume. R-matrix calculations are carried in LS coupling for th e 1S, 3P, 1D, 3F and 1G symmetries and in jj coupling for J = 0e to J = 4e. For each symmetry, an R-matrix restricted to open channels is co nstructed using a variational basis allowing the identification of the doubly excited states. From the R-matrix we deduce a scattering S-mat rix which is expressed as the sum of resonant and non-resonant parts, i.e. in a form suited to resonance analysis. The positions and autoion ization widths of 6d2 and 7p2 levels are predicted from the energy dep endence of the density of states matrix, equivalent to the time-delay matrix. The approach is connected with other theories, in particular w ith Fano's configuration interaction method which treats bound levels embedded in continua.