Photodetachment

Investigations of photon–ion interactions have grown rapidly over the past few decades, primarily due to the increased availability of laser and synchrotron light sources. At photon energies below about 1 keV, the dominant radiative process is the electric dipole induced photoelectric effect. In the gaseous phase, the photoelectric effect is referred to as either photoionization (atoms and positive ions) or photodetachment (negative ions). This chapter reviews the basics of negative ions, photodetachment, and the experimental methods used when the photodetachment process is applied to the study of negative ions. Negative ions of molecules and cluster exist, but this article covers only atomic negative ions. The monographs of Massey 1 and Smirnov 2 and a review by Bates 3 offer good introductions to the subject of negative ions. The focus will be on accelerator-based measurements. Reviews of experimental methods used to investigate the properties of negative ions have been published by, for example, Andersen 4 , Pegg 5 , and Rienstra-Kiracofe 6 .