Kinetic and thermodynamic measurements of the reactions of the positive ions, Mn + and MnOH + , formed by adding manganese to fuel-rich flames of either H 2 + O 2 or C 2 H 2 + O 2

Mass spectrometric sampling of flat, fuel-rich flames of H2 or C2H2, burning at 1 atm. and at 1800–2650 K, has revealed that the ions MnOH+ and Mn+ are present in such flames, when seeded with amounts of manganese less than 1 p.p.m. Free electrons were the only negatively charged species. The concentrations of these two positive ions were shown to be linked by the reaction MnOH+ + H = Mn+ + H2O being close to equilibrium downstream of the reaction zone of a flame, provided it was hotter than 2100 K. The equilibrium constant of this reaction was measured in flames differing in temperature; the values showed that the reaction's forward step is exothermic by 233 ± 20 kJ mol−1. This magnitude indicates that the ionisation energy of MnOH is 763 ± 35 kJ mol−1. In addition, the rate constant of the forward step was measured and found to have an activation energy of 112 ± 25 kJ mol−1.