Ionization of alkaline earth additives in hydrogen flames - II. Kinetics of production and recombination of ions

Abstract

Mass spectrometric measurements have been made of the concentrations of each ion along flames of H 2 +O 2 +N 2 seeded with trace quantities of calcium or strontium. Levels of ionization were found not to correspond to an equilibrium state of affairs. It proved possible to measure the rates of ion production and disappearance. Ions originate from one or other or both of the indistinguishable processes: M+OH → MOH + +e – , MO+H → MOH + +e – , for an alkaline earth M. Overall rate constants and their variation with temperature are presented. Activation energies equal endothermicities and cross-sections are normal. Recombination is by the dissociative process: MOH + + e – → MO+H or M+OH, which for both calcium and strontium has a rate constant close to 1x10 –7 ion –1 ml s –1 at 2000 K. This recombination coefficient decreases with increasing temperature for both alkaline earths.