Hydrogen Atom Scrambling in Ion-Molecule Reactions of Methane and Ethylene

The product distribution for the reactions ${\mathrm{CH}}_4^{+}+{\mathrm{CD}}_4\mathrm{,\hspace{0.17em}}{\mathrm{CH}}_3^{+}+{\mathrm{CD}}_4\mathrm{,\hspace{0.17em}}{\mathrm{C}}_2{\mathrm{H}}_4^{+}+{\mathrm{C}}_2{\mathrm{D}}_4,$ and their isotopic complements are determined as a function of reactant ion kinetic energy over the range from thermal energies to 10 eV. The reaction of ${\mathrm{CH}}_4^{+}$ with the parent neutral proceeds both via proton transfer and hydrogen atom abstraction accompanied by approximately 10% hydrogen atom exchange during reaction. The reactions ${\mathrm{CH}}_3^{+}+{\mathrm{CD}}_4$ and ${\mathrm{C}}_2{\mathrm{H}}_4^{+}+{\mathrm{C}}_2{\mathrm{D}}_4$ are shown to proceed with isotopic scrambling of the hydrogen atoms over the entire kinetic energy range from thermal energies to 10 eV. Several endothermic channels are observed at high kinetic energies for the reaction ${\mathrm{C}}_2{\mathrm{H}}_4^{+}+{\mathrm{C}}_2{\mathrm{D}}_4$ including the production of ${\mathrm{C}}_2{\mathrm{H}}_2^{+}\mathrm{,\hspace{0.17em}}{\mathrm{C}}_2{\mathrm{H}}_3^{+}\mathrm{,\hspace{0.17em}}{\mathrm{C}}_2{\mathrm{H}}_5^{+},$ and ${\mathrm{C}}_3{\mathrm{H}}_3^{+}$ ions.