Reactions Initiated by β Decay of Tritium. II. The Tritium-Ethylene System

Because of the β decay of tritium gas, T₂→(He³T)⁺+e, the tritium‐ethylene system undergoes reactions yielding various tritiated hydrocarbons. From the effects of three experimental variables (T₂ conc., γ irradiation, replacing T₂ by HT) on the rates of formation of tritiated compounds, we distinguished two types of labeling processes: $$\begin{array}{c}(\mathrm{a}\mathrm{)\hspace{0.17em}}\mathrm{Recoil\; labeling}\mathrm{:(}{\mathrm{He}}^3\mathrm{T}{)}^{+}+{\mathrm{C}}_2{\mathrm{H}}_4\mathrm{+(e)\to }\mathrm{Tritiated\; compounds},\\ (\mathrm{b}\mathrm{)\hspace{0.17em}\beta \hspace{0.17em}}\mathrm{labeling}:{\mathrm{T}}_2+{\mathrm{C}}_2{\mathrm{H}}_4\mathbf{\rightsquigarrow }{\displaystyle {lim}^{\mathbf{e}}}\mathrm{Tritiated\; compounds}.\end{array}$$ Formation of tritiated ethylene involved both processes; its rate was independent of temperature (25°C↔—78.5°C), and not affected by the addition of nitric oxide ([NO]/[C₂H₄]≃0.05). Tritiated ethane, propane, and n‐butane were formed exclusively by the β‐labeling process; the rate of formation of these compounds increased with decreasing temperature and nitric oxide almost completely eliminated their production. Probable mechanisms for the recoil and β‐labeling processes are discussed.