Some recent developments in the study of unstable species

The papers in this monograph reveal the considerable advances made during the past decade in the direct observation of free radicals, excited molecules, ions, and other reactive particles. These developments have followed the introduction of new techniques for producing large concentrations of these reactive species and have been facilitated by the use of relatively recent analytical devices and by the adaptation of older ones. However, to a large extent these developments are a direct consequence of the extensive studies, carried out during the past 30 years, in which the chemical properties of free radicals have been inferred primarily from an analysis of their chemical reaction products. These older methods are more indirect, but both approaches are required for a detailed understanding of unstable species and their reactions