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Photodetachment of Al-(3s23p23 3P) 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(3s24s2S), 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 (3s24s4p3P0) character. Density plots of the resonance state are presented to demonstrate its structure. Near the Al(3s23p2P) threshold, theory agrees also with recent relative measurements of D. Calabrese et al. [Phys. Rev. A 54, 2797 (1996)].