Photolysis of Ethylene at 1048–1067 Å. Reactions of C2H4+ and Fragmentation of the Superexcited Ethylene Molecule

C₂H₄–NO, C₂H₄–O₂ and C₂H₄–(CH₃)₂NH–O₂ mixtures have been irradiated with an argon resonance lamp emitting only the 1048‐ and 1067‐Å lines. The ionization efficiency ratios: ηC₂D₄/η_NO, ηC₂H₄/η_NO, ηC₂D₄/ηC₂H₄ were determined to be 0.30±0.003, 0.27±0.003 and 1.12, respectively. trans‐2‐Butene and cis‐2‐butene are major products when NO (I.P.=9.25 eV) or (CH₃)₂NH (I.P.=8.24 eV) are added to C₂H₄. Radiation of pure C₂H₄ or of C₂H₄–O₂ mixtures yielded only minor traces of 2‐C₄H₈. In accord with earlier radiolysis studies we ascribe the formation of 2‐C₄H₈ to the charge‐transfer process $${\mathrm{C}}_4{\mathrm{H}}_8^{+}+\mathrm{NO}\mathrm{\hspace{0.17em}(}\mathrm{or}\mathrm{\hspace{0.17em}(}{\mathrm{CH}}_3{)}_2\mathrm{NH}\mathrm{)\to }{\mathrm{C}}_4{\mathrm{H}}_8+{\mathrm{NO}}^{+}\mathrm{\hspace{0.17em}(}\mathrm{or}\mathrm{\hspace{0.17em}(}{\mathrm{CH}}_3{)}_2{\mathrm{NH}}^{+}\mathrm{),}$$ where C₄H₈⁺ may possess some excess internal energy carried over from the exothermic condensation reaction (C₂H₄^*)⁺+C₂H₄→(C₄H₈^*)⁺. For a constant C₂H₄–NO mixture M(C₄H₈)/N increases drastically with an increase of the pressure of C₂H₄ from 0.1 to 6 torr. Also, in pure C₂H₄, M(CH₃)/N which is close to unity at 0.5 torr is seen to diminish to 0.2 when the pressure is raised to 29.8 torr. These effects are largely ascribed to a competition between decomposition and stabilization of the [C₄H₈^*]⁺ product ion. A rate constant of 10⁷ sec⁻¹ is derived for the unimolecular decomposition of (C₄H₈^*)⁺ assuming that stabilization occurs at every collision with C₂H₄. It is shown that Ne is about 100 times less efficient than C₂H₄ in stabilizing (C₄H₈^*)⁺. The superexcited C₂H₄^* dissociates as follows, C₂H₄^*→C₂H₂+H₂ and C₂H₄^*→C₂H₂+2H. Isotopic analysis of the hydrogen formed in the photoionization of CH₂CD₂ shows that the relative probabilities for the elimination of H₂, HD, and D₂ from CH₂CD₂^* are the same for the superexcited molecule as for the excited molecule formed by absorption of 8.4‐ to 10‐eV photons.