Eigenchannel R-matrix calculation of the photoabsorption spectrum of strontium

Abstract

Presents the first detailed theoretical calculation of the absorption spectrum of Sr out of the 5s2 1S0 ground state. The autoionisation region below the 5p3/2 threshold is investigated, photoionisation cross sections being calculated by combining the multichannel quantum defect theory (MQDT) with the eigenchannel R-matrix method. Small-scale variational R-matrix calculations enable one to evaluate LS-coupled short-range reaction matrices. A jj-coupled reaction matrix is then deduced using a geometrical frame transformation. Diagonalisation of this matrix gives the energy-dependent MQDT parameters required for the description of the 13 relevant interacting channels. The 13-channel MQDT model built with theoretical R-matrix parameters provides an accurate description of the positions and the shapes of the 4d3/2,5/2 np, nf and 5p1/2,3/2 ns, nd J=1 autoionising lines. Particular attention is paid to high lying resonances observed near the spin-orbit split 4d3/2,5/2 and 5p1/2,3/2 thresholds.