IONIZATION IN PREMIXED FUEL-LEAN FLAMES OF H-2, O-2 AND N-2 .2. IONS FROM ALKALI-METAL ADDITIVES

Mass spectrometric measurements have shown that the charged species in an oxygen-rich flame are mainly H3O+ and the free electron. These ions are most probably produced via H + OH reversible arrow= H2O* (6) H2O* + H --> H3O+ + e(-) (7) where H2O* is excited, either vibrationally or electronically. The fact that the concentrations of the radicals H and OH early in such a flame exceed their values for final equilibrium, leads to the initial generation of ions being relatively rapid. When the alkali metals, Na or K, are added to the flame, Na+ and K+ appear much more quickly than can be explained by thermal ionisation, which dominates the production of ions from alkali metals in fuel-rich flames. The explanation appears to be the hitherto unsuspected reaction: H2O* + A --> A(+).H2O + e(-) (8) A(+) H2O + M = A(+) + H2O + M where A = Na or K. Kinetic parameters have been derived for many of these processes, and are presented. Alternative explanations, e.g. K + OH --> K+ + OH- or K + H3O+ --> KC + H2O + H, are not able to account for the rapid production of ions. It is also concluded that the H2O* participating in reactions (6) and (7) is most probably in an antibonding electronic state.