Temperature and Pressure Effects in the Addition of H Atoms to Propylene

The effect of He pressure on the rate of addition of hydrogen atoms to propylene was measured at 298°K. H‐atom concentration was measured by the method of resonance fluorescence of Lyman $\alpha$ radiation at 121.6 nm. The results are consistent with the ${\text{1\hspace{0.17em}/\hspace{0.17em}p}}^{\text{1/2}}$ dependence of $k_{\mathrm{bi}}$ recently observed in the H‐atom–ethylene system. The limiting high‐pressure rate constant obtained in this work is H+C₃H₆→C₃H₇, $k_1{\text{\hspace{0.17em}=\hspace{0.17em}1.61\hspace{0.17em}±\hspace{0.17em}0.04\hspace{0.17em}×\hspace{0.17em}10}}^{\text{−12}}{\mathrm{cm}}^3{\mathrm{molecule}}^{\text{−1}}·{\sec }^{\text{−1}}$ . The temperature dependence of the H‐atom addition was investigated at 50 torr total pressure over the temperature range 177–473°K. Analysis of the data below room temperature gives the following Arrhenius parameters for addition to the terminal olefinic position: $k_{\mathrm{bi}}^{50}{\text{\hspace{0.17em}=\hspace{0.17em}(10.18\hspace{0.17em}±\hspace{0.17em}0.26)\hspace{0.17em}×\hspace{0.17em}10}}^{\text{−12}}\exp \text{[−\hspace{0.17em}(1211\hspace{0.17em}±\hspace{0.17em}11)\hspace{0.17em}/\hspace{0.17em}1.987T]}{\mathrm{cm}}^3{\mathrm{molecule}}^{\text{−1}}·{\sec }^{\text{−1}}$ . Deviations from this dependence above 298°K can be assigned to nonterminal addition, H‐atom abstraction, and increased decomposition of the excited propyl radicals.