Electron Attachment and Compound Formation in Flames. V. Negative Ion Formation in Flames Containing Chromium and Potassium

Abstract

Application of several different experimental techniques (flame‐ion mass spectrometry, microwave cavity resonance, electrostatic probe, and absorption spectrophotometry) reveals that addition of chromium to fuel‐rich atmospheric‐pressure H₂/O₂/N₂ flames seeded with potassium results in formation of Cr‐containing negative ions. The following reaction scheme, equilibrium constants, and enthalpy changes provide a satisfactory quantitative interpretation of the experimental results: $\mathrm{e+}{\mathrm{HCrO}}_3={\mathrm{CrO}}_3^{-}+\mathrm{H}{\mathrm{,\hspace{0.17em}\Delta \; H}}_{\text{0,1}}\text{°=125± 40\hspace{0.17em}}{\mathrm{kJ\; mole}}^{\text{−1}}\mathrm{,\hspace{0.17em}}{\mathrm{H}}_2+{\mathrm{CrO}}_3^{-}={\mathrm{HCrO}}_3^{-}+\mathrm{H}{\mathrm{,\hspace{0.17em}\Delta \; H}}_{\text{0,4}}\text{°=78± 40\hspace{0.17em}}{\mathrm{kJ\; mole}}^{\text{−1}}{\mathrm{\hspace{0.17em}K}}_1\text{=2500\hspace{0.17em}}\exp {\text{(−13\hspace{0.17em}400/T)\hspace{0.17em}K}}_4\text{= 1.7\hspace{0.17em}}\exp \text{(−9900/T).}$ Electron affinities for HCrO₃ and CrO₃ inferred from this data are 229 kJ mole⁻¹ and 390 kJ mole⁻¹, respectively.