Studies of Plasma Reaction Processes Using a Flowing-Afterglow/Langmuir Probe Apparatus

Abstract

As recently as some twenty five years ago even the order-of-magnitude of the thermal energy rate coefficient, k, for any ion-molecule reaction could not be quoted with conviction, and the forms of the temperature variations of rate coefficients were quite unknown. The first reliable data under well- defined conditions, were obtained using stationary afterglow techniques [1], but a truly dramatic increase in the understanding of thermal energy ion- molecule reactions resulted from the development and exploitation of the flowing afterglow technique by E.E. Ferguson, F.C. Fehsenfeld and A.L. Schmeltekopf in 1964 [2,3]. During the first few years, flowing afterglows were operated only at room temperature and the k were determined!for a large number of different types of ion-molecule reactions (e.g. charge transfer, proton transfer, etc.). These studies showed that the large majority of exoergic binary (two-body) ion-molecule reactions proceeded rapidly at room temperature , i.e. k~kc (the collisional rate coefficient). For non-polar molecules, kc is the classical collision (Langevin) rate coefficient [4]; for polar molecules, kc is somewhat greater [5].