Radiofrequency resonance study of alkali metal ionization in a carbon monoxide flame. Part 2.—Determination of the ionization rate constants for caesium, potassium, sodium and lithium

Abstract

The collisional alkali-ionization rate constants, k_i, for an atmospheric-pressure CO/O₂/N₂ flame of well-known temperature (1930 K) and composition have been redetermined using the r.f. resonance method. The values of k_i were obtained from the r.f. bandwidth measured as a function of risetime. Hydroxide formation was found to play a substantial role in the case of lithium only. Attention is given to the mathematical procedure which enabled the simultaneous determination of the sensitivity of the r.f. resonance system (whose design and performance were described in Part 1) as well as the value of k_i; in the case of Li, where the association factor ϕ[LiOH]/[Li] appeared to depend upon height, a different procedure was necessary. Our experimental values of k_i, which are found to be independent of alkali concentration, are: k_i(Cs)= 0.47 × 10², k_i(K)= 13.4, k_i(Na)= 0.30 and k_i(Li)= 0.13 s^–1. These values are compared critically with the results from literature; within this context we discuss to what extent chemi-ionization, electron attachment, (ambipolar) diffusion and hydroxide formation may be responsible for systematic errors.