An Experimentalist's View of the H− Ion

Abstract

AbstractWe present a short survey of selected experimental studies of the negative ion of hydrogen over the past twenty‐three years at the 800 MeV linear accelerator at Los Alamos. Experimental techniques are described and heuristic models are used to explain and motivate experimental results. We discuss the first observations of the 1P resonances just below n = 2, the so‐called “Feshbach” and “shape” resonances, seen in photodetachment. As one experimental question is answered, another question becomes exposed, for example, the effects of electric fields on the spectroscopy of the ion. Techniques used to convert the H− ion into a dual‐beam interferometer moving near the speed of light are described. Experimental data taken near thresh old in an electric field are displayed on a universal plot. Multiphoton detachment extends the spectroscopy of the ion to singlet states that would be unreachable by single photodetachment processes. A thin foil also is used to probe the ion structure. Using ion beams in the 35 kV range, 2‐photon measurements of an isotope shift between Hand D− reveal two‐electron correlation consequences. Finally we ad dress the question, “Why has the shape resonance not been seen in astrophysical observations?