Pulse Radiolysis Studies. XX. Kinetics of Some Addition Reactions of Gaseous Hydrogen Atoms by Fast Lyman-α Absorption Spectrophotometry

The pulse radiolysis technique combined with fast Lyman‐α absorption spectrophotometry, has been used to study the kinetics of several addition reactions of gaseous hydrogen atoms. The following absolute rate constants, at 298°K, have been obtained: $$\mathrm{H}+{\mathrm{O}}_2+\mathrm{Ar}={\mathrm{HO}}_2+\mathrm{Ar}{\text{, (5.9\hspace{0.17em}±\hspace{0.17em}0.7)\hspace{0.17em}×\hspace{0.17em}10}}^9{M}^{\text{−2}}·{\sec }^{\text{−1}},$$ $$\mathrm{H}+\mathrm{CO}+{\mathrm{H}}_2=\mathrm{HCO}+{\mathrm{H}}_2{\text{, (4.0\hspace{0.17em}±\hspace{0.17em}0.6)\hspace{0.17em}×\hspace{0.17em}10}}^7{M}^{\text{−2}}·{\sec }^{\text{−1}},$$ $$\mathrm{H}+\mathrm{CO}+\mathrm{Ar}=\mathrm{HCO}+\mathrm{Ar}{\text{, (2.6\hspace{0.17em}±\hspace{0.17em}0.4)\hspace{0.17em}×\hspace{0.17em}10}}^7{M}^{\text{−2}}·{\sec }^{\text{−1}},$$ $$\mathrm{H}+\mathrm{NO}+{\mathrm{H}}_2=\mathrm{HNO}+{\mathrm{H}}_2{\text{, (1.4\hspace{0.17em}±\hspace{0.17em}0.2)\hspace{0.17em}×\hspace{0.17em}10}}^{10}{M}^{\text{−2}}·{\sec }^{\text{−1}}.$$ These results, and our earlier value for $k_1$ with H₂ as third body, give values of $k_1^{H_2}{\mathrm{\hspace{0.17em}/\hspace{0.17em}k}}_1^{\mathrm{Ar}}\text{\hspace{0.17em}=\hspace{0.17em}2.9}$ and $k_2^{H_2}{\mathrm{\hspace{0.17em}/\hspace{0.17em}k}}_2^{\mathrm{Ar}}\text{\hspace{0.17em}=\hspace{0.17em}1.5}$ for the relative third‐body efficiencies of hydrogen and argon. The high‐pressure limiting rate constant for H‐atom addition to ethylene, obtained directly in the high‐pressure region, was found to be $$\mathrm{H}+{\mathrm{C}}_2{\mathrm{H}}_4={\mathrm{C}}_2{\mathrm{H}}_5{\text{*, (5.5\hspace{0.17em}±\hspace{0.17em}0.5)\hspace{0.17em}×\hspace{0.17em}10}}^8{M}^{\text{−1}}·{\sec }^{\text{−1}},$$ with both H₂ and Ar as third body.