A Personal history of the early development of the flowing afterglow technique for ion-molecule reaction studies

A personal perspective of the historical development of the flowing afterglow (FA) technique for measuring thermal energy ion-molecule reaction rate constants is presented. The technique was developed in the period starting in late 1962 in what was then the National Bureau of Standards in Boulder, Colorado. The motivation was primarily to obtain a quantitative understanding of the ion chemistry of the terrestrial ionosphere, a program that was substantially achieved. The thermal energy measurements were extended in temperature from 300 K to a range of 80 K-900 K and subsequently to a center-of-mass kinetic energy range up to ∼ 2 eV with the introduction of a drift tube into the FA.The chemical versatility, in regard to both the ion and the neutral reactants measured, remains unequaled and FA systems are currently in widespread use around the world for a variety of chemical research programs.