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; ${\mathrm{\Delta H}}_0\text{°\hspace{0.17em}=\hspace{0.17em}−\hspace{0.17em}40\hspace{0.17em}±\hspace{0.17em}40}{\mathrm{kJ\; mol}}^{\text{−1}},{\mathrm{H}}_2{\mathrm{WO}}_4{\mathrm{+e}}^{-}\leftrightarrows {\mathrm{HWO}}_4^{-}+\mathrm{H}{\mathrm{;\; \Delta H}}_0\text{°\hspace{0.17em}=\hspace{0.17em}+\hspace{0.17em}40\hspace{0.17em}±\hspace{0.17em}40}{\mathrm{kJ\; mol}}^{\text{−1}},{\mathrm{HWO}}_4^{-}+\mathrm{H}\leftrightarrows {\mathrm{WO}}_3^{-}+{\mathrm{H}}_2\mathrm{O}{\mathrm{;\; \Delta H}}_0\text{°\hspace{0.17em}=\hspace{0.17em}−\hspace{0.17em}22\hspace{0.17em}±\hspace{0.17em}40}{\mathrm{kJ\; mol}}^{\text{−1}}$ . The enthalpy changes imply electron affinities for WO₃ and HWO₄ of approximately 351 and 420 kJ mol⁻¹, respectively.