Dissociation of Propane, Propylene and Allene by Electron Impact

The appearance potentials of all the ions from ${\mathrm{C}}_3$ $\mathrm{H}_8^{}{}_{}{}^{+}$ to ${\mathrm{C}}_3$ $\mathrm{H}_2^{}{}_{}{}^{+}$ and ${\mathrm{C}}_2$ $\mathrm{H}_5^{}{}_{}{}^{+}$ to ${\mathrm{C}}_2$ $\mathrm{H}_2^{}{}_{}{}^{+}$ that result from the bombardment of propane, propylene and allene have been measured. Although little is known concerning the energies of the various free radicals formed, it is still possible to specify uniquely most of the reactions which lead to the observed ions. This knowledge in turn allows upper limits to be placed on the ionization potentials of the free radicals themselves. These limits range from about 9 to 12 volts, showing that the ionization potentials of these radicals do not differ greatly from one another.