K-Shell Photodetachment of He^-: Experiment and Theory

High-resolution K-shell photodetachment measurements of He^- giving rise to He⁺ ions have been performed using a merged synchrotron vacuum ultraviolet photon-ion beam technique. The measurements on this fundamental negative ion display dramatic structure differing substantially, qualitatively and quantitatively, from the corresponding process in neutral atoms and positive ions, owing to the dominance of correlation in both initial and final states of He^-. In addition, this experimental investigation provides an unambiguous test of two independent theoretical calculations that report serious discrepancies and shows excellent agreement with one of them.