Observation of resonance structure in the Na^- photodetachment cross section

We have used a collinear laser-ion beam apparatus to investigate the partial cross section for the photodetachment of Na^- via the Na(4s)+e^-(εp) channel. The measured cross-section spectrum is compared to a recent R-matrix calculation [C.-N. Liu and A. F. Starace, preceding paper, Phys. Rev. A 59, 3643 (1999)]. The photodetachment cross section was measured in the energy range 4.657–4.880 eV. In this spectrum, we have identified four resonances that converge on the Na(4d) threshold. The energies and widths of the resonances were determined from the measured cross section. A semiempirical formula has also been used to predict the positions of the four resonances and to show that, in a semiclassical model, the resonances belong to the same ¹P^o series.