  We present the results of experimental studies of photon-negative ion
interactions involving the dynamics of two electrons. Resonances associated
with doubly excited states of Li^- and He^- have been observed using laser
photodetachment spectroscopy. Total and partial photodetachment cross sections
have been investigated. In the former case, the residual atoms are detected
irrespective of their excitation state, while in the latter case only those
atoms in specific states are detected. This was achieved by the use of a state
selective detection scheme based on the resonant ionization of the residual
atoms. In addition, in the case of Li^- photodetachment, the threshold behavior
of the Li(2 ^2P)+e^-(ks) partial cross section has been used to accurately
measure the electron affinity of Li.
