MOLECULAR-BEAM STUDIES OF PENNING IONIZATION

Molecular-beam experiments have exposed a new wealth of detail on the general reaction A+B-->A+B++e- first suggested by Penning in 1927. Th e new capabilities not available to traditional swarm techniques inclu de mass and electron spectroscopy on the reaction products and angle-r esolved measurements of the scattering of both reagents and products. These new results have stimulated the recent development of both the e lectronic structure and the dynamical theories necessary for a first-p rinciples description of at least the simplest of these reactions, tho se involving small atomic and diatomic species B. Recent progress in b oth experiment and interpretation is critically reviewed, and the pros pects for attaining a global understanding of Penning ionization in la rger systems are