Electron Attachment and Compound Formation in Flames. III. Negative Ion and Compound Formation in Flames Containing Tungsten and Potassium

Application of several different experimental techniques (flame-ion mass spectrometry, microwave cavity resonance, electrostatic probe, and absorption spectrophotometry) reveals that addition of tungsten to fuel-rich atmospheric-pressure H2/O2/N2 flames seeded with potassium results in reductions in concentrations of free potassium atoms and in formation of stable W-containing negative ions. The following reaction scheme and enthalpy changes provide a satisfactory quantitative interpretation of the experimental results: K+H2WO4⇆KHWO4+H; ΔH0° = − 40 ± 40 kJ mol−1, H2WO4+e−⇆HWO4−+H; ΔH0° = + 40 ± 40 kJ mol−1, HWO4−+H⇆WO3−+H2O; ΔH0° = − 22 ± 40 kJ mol−1. The enthalpy changes imply electron affinities for WO3 and HWO4 of approximately 351 and 420 kJ mol−1, respectively.