Observation of resonance structure in the Na- photodetachment cross section

We have used a collinear laser-ion beam apparatus to investigate the partia l cross section for the photodetachment of Na- via the Na(4s) + e(-)(epsilo n p) 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 res onances that converge on the Na(4d) threshold. The energies and widths of t he resonances were determined from the measured cross section. A semiempiri cal formula has also been used to predict the positions of the four resonan ces and to show that, in a semiclassical model, the resonances belong to th e same P-1(o) series. [S1050-2947(99)10805-9].