RESONANCE FEATURE IN AL- PHOTODETACHMENT BELOW THE AL(3S(2)4S-S-2) THRESHOLD

Photodetachment of Al-(3s(2)3p(23)P) near the threshold of the first e xcited 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 d etected. Measurements just below the threshold of the first excited st ate, Al(3s(2)4s S-2), find a large resonance peak in the detachment si gnal. An eigenchannel R-matrix calculation generates a resonance struc ture that is qualitatively similar to the data and identifies the larg e 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 t he 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)].