Molecular-beam studies of Penning ionization

Molecular-beam experiments have exposed a new wealth of detail on the general reaction ${A}^{*}+B\ensuremath{\rightarrow}A+{B}^{+}+{e}^{\ensuremath{-}}$ first suggested by Penning in 1927. The new capabilities not available to traditional swarm techniques include mass and electron spectroscopy on the reaction products and angle-resolved measurements of the scattering of both reagents and products. These new results have stimulated the recent development of both the electronic structure and the dynamical theories necessary for a first-principles description of at least the simplest of these reactions, those involving small atomic and diatomic species $B$. Recent progress in both experiment and interpretation is critically reviewed, and the prospects for attaining a global understanding of Penning ionization in larger systems are assessed.

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