Resonance feature in Al 2 photodetachment below the AlÑ3s 2 4s 2 SÖ threshold

Observations of the properties of doubly excited autoionizing states in multielectron systems can provide detailed information on electron-electron correlations and stringent experimental checks for multielectron theory. One of the most interesting and demanding processes available for these studies is the photoexcitation of doubly excited negative ions in negative-ion photodetachment. Photoexcitation provides precise control of the excitation energy and final states ~via the dipole selection rules!, while negative ions allow the opportunity to observe electron-electron correlation which is not masked by the Rydberg levels typical of neutral atom or positive ion spectra. Several studies of doubly excited negative ion states have been undertaken by observing resonance structure in the total detachment cross section. These resonances result from the interference between the continuum detachment channel and the detachment through the autoionizing state, as described by Fano in 1961 @1#. To date, the most thorough investigation of these resonances is for the hydrogen negative ion. These studies include measurements of the cross section for photodetachment from H 2 near the thresholds for excitation to the first several excited states of H @2‐4#, revealing a