Atom–Molecule Kinetics Using ESR Detection. V. Results for O+OCS, O+CS2, O+NO2, and H+C2H4

The wide‐temperature‐range, fast‐flow reactor with ESR detection used in previous papers of this series has been further improved so that rate coefficients of nearly 10¹³ cm³ mole⁻¹·sec⁻¹ can now be measured by the pseudo‐first‐order method. Results have been obtained over the temperature range 273°–808°K for the reaction $$\mathrm{O+OCS\to CO+SO,}$$ over 227°–538°K for $${\mathrm{O+CS}}_2\mathrm{\to CS+SO,}$$ and over 297°–543°K for $${\mathrm{O+NO}}_2{\mathrm{\to NO+O}}_2$$ In Arrhenius form the rate coefficients are (cm³ mole⁻¹·sec⁻¹) $$k_1{\text{\hspace{0.17em}=\hspace{0.17em}1.9\hspace{0.17em}×\hspace{0.17em}10}}^{13}\exp {\text{(−\hspace{0.17em}4530\hspace{0.17em}/\hspace{0.17em}RT); k}}_2{\text{\hspace{0.17em}=\hspace{0.17em}1.2\hspace{0.17em}×\hspace{0.17em}10}}^{13}\exp {\text{(−\hspace{0.17em}1050\hspace{0.17em}/\hspace{0.17em}RT); k}}_3{\text{\hspace{0.17em}=\hspace{0.17em}1.0\hspace{0.17em}×\hspace{0.17em}10}}^{13}\exp \text{(−\hspace{0.17em}580\hspace{0.17em}/\hspace{0.17em}RT).}$$ The product SO in [1] and [2] was measured in its ${}^3\Sigma$ ground state, and excited vibrational states could not be detected by ESR under our experimental conditions, although the SO must have been so excited initially. Stoichiometry and mechanisms are discussed. The H + C₂H₄ reaction was also measured in room‐temperature helium and argon, and in helium at 525°K. The data were obtained over a pressure range of about 0.5–2.5 mm, and the pressure dependence of the net rate coefficient $k_t$ for H‐atom decay was clearly measurable. Mass spectrometer analysis showed essentially all of the C₂H₄ to be converted to C₂H₆ and CH₄. The mechanism is discussed. From the $P^{\text{−1}}\text{\hspace{0.17em}=\hspace{0.17em}0}$ intercept of plots of $k_t^{\text{−1}}$ vs $P^{\text{−1}}$ , the data were assumed to yield values of the rate coefficient $k_4$ for the initial step H + C₂H₄→C₂H₅*, i.e., the production of vibrationally excited C₂H₅* in the Rabinovitch manner. At room temperature the helium data give $k_4{\text{\hspace{0.17em}=\hspace{0.17em}2.2\hspace{0.17em}×\hspace{0.17em}10}}^{11}$ and the argon data ${\text{1.4\hspace{0.17em}×\hspace{0.17em}10}}^{11}{\mathrm{cm}}^3{\mathrm{mole}}^{\text{−1}}·{\sec }^{\text{−1}}$ . From the slopes of the two plots the probability for transfer of vibrational energy from C₂H₅* to translation of argon is found to be about five times greater than for helium. The limited high‐temperature data imply very little temperature dependence for either $k_4$ or its reverse.