Mass-Spectrometric Investigation of the Reactions of O Atoms with H2 and NH3

Abstract

The reaction of H₂ with O in the absence of O₂ was studied in the temperature range 400° to 600°K by using a stirred reactor with a mass spectrometer for analysis. The rate constant for the H₂+O→OH+H reaction was found to be ${\text{4.3×10}}^{13}\hspace{0.17em}\exp \text{(−10\hspace{0.17em}200/RT)\hspace{0.17em}}\mathrm{cc}/\mathrm{mole}·\sec$ . The rate of O consumption was about three to five times smaller in the absence of O₂ than in its presence. This difference was quantitatively explained as a result of the reaction sequence $$\begin{array}{c}\mathrm{H}+{\mathrm{O}}_2+\mathrm{M}\to {\mathrm{HO}}_2+\mathrm{M};\\ {\mathrm{HO}}_2+\mathrm{O}\to \mathrm{OH}+{\mathrm{O}}_2.\end{array}$$ The reaction of NH₃ with O in the absence of O₂ was also studied for the temperature range 350° to 600°K. The stoichiometry of the reaction could be approximately represented by $${\mathrm{NH}}_3\text{+4.4}\mathrm{O}\to \mathrm{NO}\text{+0.5}{\mathrm{H}}_2\text{+1.2}{\mathrm{O}}_2\text{+1.0}{\mathrm{H}}_2\mathrm{O}.$$ In contrast to the H₂+O reaction, the rates for consumption of O were not affected by the presence or absence of excess O₂ within experimental error. A reaction mechanism was proposed, and using this mechanism the rate constant for the NH₃+O→NH₂+OH reaction was estimated to be ${\text{1×10}}^{12}\hspace{0.17em}\exp \text{(−4800/RT)\hspace{0.17em}}\mathrm{cc}/\mathrm{mole}·\sec$ .