Resonance feature in Al- photodetachment below the Al(3s(2)4s(2)S) threshold

Photodetachment of Al-(3s(2)3p(23)P) near the threshold of the first excited state of neutral aluminum has been studied both experimentally and theoretically. A 19-keV mass-resolved Al- beam was intersected by a frequency-doubled neodymium-doped yttrium aluminum garnet pumped dye-laser beam, and the fast atoms created by detachment processes were detected. Measurements just below the threshold of the first excited state, Al(3s(2)4s S-2), find a large resonance peak in the detachment signal. An eigenchannel R-matrix calculation generates a resonance structure that is qualitatively similar to the data and identifies the large resonance peak as resulting from a doubly excited negative-ion state having predominantly (3s(2)4s4p (3)p(o)) character. Density plots of the resonance state are presented to demonstrate its structure. Near the Al(3s(2)3p P-2) threshold, theory agrees also with recent relative measurements of D. Calabrese et al. [Phys. Rev. A 54, 2797 (1996)].