KINETICS OF GAS-PHASE IONIZATION OF AN ALKALI-METAL, A, BY THE ELECTRON AND PROTON-TRANSFER REACTIONS - A-]A(+).H2O+H, AOH+H3O+-]AOH(2)(+)+H2O IN FUEL-RICH FLAMES AT 1800-2250K(H3O+)

Fuel-rich flames of H-2 + O-2 + N-2 have been burned with trace quanti ties of an alkali metal, Li, Na or K. In general, these additives exis t mainly as free atoms A of the metal and also molecules of the hydrox ide AOH in the gas phase. Without alkali metal, the major charged spec ies are free electrons and H3O+. With an alkali metal added, the exoth ermic reactions: H3O+ + A --> A(+) . H2O + H (3) H3O+ + AOH --> AOH(2) (+) + H2O (4) occur. Mass spectrometric measurements of ion concentrat ions along these well defined flat flames, in which there is plug flow , enabled the rate constants of reactions (3) and (4) to be measured a t different temperatures. Reaction (4) involves proton transfer from t he ion H3O+ to the polar molecule AGH; the product, protonated AGH, is mass spectrometrically indistinguishable from A(+) . H2O and it is co ncluded that A(+) . H2O and AOH(2)(+) are identical. The rate constant , k(4), of the exothermic reaction (4) is found to vary with temperatu re as T-2+/-1 ;its magnitude is largest for KOH and smallest for LiOH. The rate constant, k(3),for reaction (3), also exothermic, is larger than k(4) for the same metal, k(3) does not vary from metal to metal, but its measured temperature dependence corresponds to T-5+/-3. It is concluded that reaction (3) involves electron transfer from an alkali metal atom to the ion H3O+; this explains why k(3) > k(4) for each met al at a particular temperature. Detailed expressions, describing the t emperature-dependence of both k(3) and k(4), are deduced.