Ionization and Dissociation by Electron Impact: The Methyl and Ethyl Radicals

The lead tetra-alkyls, Pb(CH₃)₄ and Pb(C₂H₅)₄, were decomposed to yield free methyl and ethyl radicals in a specially designed furnace built into the ionization chamber of a 180^∘{} mass spectrometer tube. From the initial breaks of the ionization efficiency curves of the ions, CH₃^_⁺ and C₂H₅^{}{}_{}{}⁺$, we have found the ionization potentials of the methyl and ethyl radicals to be ${I}ᵥₑᵣₜ({CH}₃)={10.0}₀±{}0.1$ ev and ${I}ᵥₑᵣₜ({C}₂{H}₅)={8.6}₀±{}0.1$ ev. These values are in excellent agreement with those found by indirect calculations from other electron impact data on hydrocarbons. Some of the implications of these results are briefly discussed.