NEAR-THRESHOLD PHOTOIONIZATION FROM THE SR-I (5S5P) P-1(1)O STATE

Absolute photoionization cross sections from the laser-excited Sr I(5s 5p) P-1(1)0 state are reported showing a giant resonance with a peak c ross section of 5600 Mb. The absolute calibration was obtained with a saturation method as published by Burkhardt et al. In the present stud y, however, the spatial distribution of the photons in the laser pulse was measured with a cco camera and applied in the evaluation procedur e as a Gauss profile. The uncertainties in the absolute values are est imated to be less than 20%. Based on a 12-state non-relativistic close -coupling R-matrix calculation, the giant resonance is assigned as pre dominantly (5p(2)) D-1(2) with a strong admixture of(4d(2)) D-1(2). Wh ile an ab initio calculation including only discrete physical target s tates was unable to reproduce the resonance structure correctly, reaso nable agreement between experiment and theory was obtained by a semi-e mpirical simulation of additional short-range correlation and relaxati on effects.