Mass spectrometric sampling of flat, fuel-rich flames of H-2 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 +/- 135 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). In a simple flame of H-2 O-2 N-2, ions were produced from the major species containing manganese, i.e. MnO and atomic Mn, by chemi-ionisation in: MnO + H -> MnOH+ e(-) and Mn + OH -> MnOH+ + e(-). Free atoms of Mn were roughly three times as abundant as molecules of MnO. The kinetics of these chemi-ionisation reactions were measured; the reactions resulted in elevated levels of ionisation because of a flame having concentrations of the free radicals H and OH in excess of those for equilibrium. In flames of C2H2, their significant natural ionisation was transferred to the metallic additive by: H3O+ + MnO -> MnOH+ + H2O and also H3O+ Mn -> Mn+center dot H2O -> H, followed by Mn+center dot H2O -> Mn+ + H2O. These processes led to the level of ionisation early in a hydrocarbon flame being well above that for equilibrium, which was approached by ions recombining in MnOH+ +e(-) -> MnO + H or Mn + OH, as well as in the three-body reaction: Mn+ +e(-) + M -> Mn + M. Recombination coefficients were measured for these processes, as well as for MnOH+ + Cl- -> Mn + OH + CI and Mn+ + Cl- + M -> Mn + CI + M. (C) 2017 Published by Elsevier Inc. on behalf of The Combustion Institute.