AbstractHydrogen atoms from the mercury photosensitized decomposition of hydrogen was allowed to interact with ethylene. Product distributions of this interaction were analyzed with the FID‐gas‐chromatographic technique. Such distribution has been used to interprete, based on a proposed mechanism, the pressure effect on the following chemically activated process:\documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c} {H + C_2 H_5 \to C_2 H_6 *} \hfill & {2CH_3 } \hfill \\ {} \hfill & {C_2 H_6 } \hfill \\\end{array} $$\end{document}kPat 35°C has been determined to be 1.7×10‐7sec‐1from this observed pressu