Reaction of Hydrogen Atoms with C2H4 and C2D4

Abstract

A study of the photolysis of HI in the presence of C₂H₄ and C₂D₄ was carried out at low conversions, in the presence of large pressures of moderator, and at various temperatures. In the experiments with C₂D₄ the formation of small percentage of HD was detected and it was found that the HD/H₂ ratio provides a very sensitive test of the presence of hot reactions. The observed rate of hydrogen formation was used to evaluate the ratio of rate constants for the following reactions: $$\mathrm{H}+\mathrm{HI}\to {\mathrm{H}}_2+\mathrm{I},$$ $$\mathrm{H}+{\mathrm{C}}_2{\mathrm{H}}_4{\mathrm{or\; C}}_2{\mathrm{D}}_4\to {\mathrm{C}}_2{\mathrm{H}}_5{\mathrm{or\; C}}_2{\mathrm{D}}_4\mathrm{H}.$$ The Arrhenius parameters for $k_2{\mathrm{\hspace{0.17em}/\hspace{0.17em}k}}_1$ were found to be $\text{0.30}\exp \text{(−\hspace{0.17em}845\hspace{0.17em}/\hspace{0.17em}RT)}$ and, using the previously determined value for $k_1$ , we find $k_2{\text{\hspace{0.17em}=\hspace{0.17em}6.9\hspace{0.17em}±\hspace{0.17em}0.7\hspace{0.17em}×\hspace{0.17em}10}}^{11}{\mathrm{cm}}^3{\mathrm{mole}}^{\text{−1}}·{\sec }^{\text{−1}}$ . This value is based actually on the value of $k$ for H+I₂ as determined by Sullivan and extrapolated to our conditions. C₂D₄ has been found to react about 10% faster than C₂H₄.