Abstract
The cross sections for the photodetachment from a weakly bound positronium negative ion Ps- below the threshold for the formation of Ps(n = 4) are calculated using the hyperspherical close-coupling method, and are compared with the corresponding spectra for the H- ion. Detailed resonance structures in the spectra near the Ps(n = 2, 3 and 4) thresholds are reported for the first time. The off-resonance cross section below the Ps(n = 2) threshold differs appreciably from that obtained by a variational calculation (Ward et al 1987 J. Phys. B: At. Mol. Phys. 20 127), but agrees well with the recent close-coupling calculations with a B-spline expansion (Igarashi et al 2000 Phys. Rev. A 61 032 710). The resonance energies and widths of the 1Po symmetry are generally in good agreement with the results of the complex-coordinate rotation calculation.
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Received 10 May 2000, online 23 August 2000