Formation of positive ions of quadricyclane

Quadricyclane (QC) is one of the strained hydrocarbons that have potential as high-energy density materials used as aerospace fuel or as additives to kerosene rocket fuel. We have studied the formation of positive ions of QC by electron impact and by charge-transfer reactions, using Fourier-transform mass spectrum (FTMS) techniques. The electron ionization cross sections in the energy range of 10-200 eV have been measured. The total cross section reaches a maximum of 2.3x10$^{-15}$ cm$^{2}$ at 60 eV. Parent ion C$_{7}$H$_{8}^{+}$ and 21 fragment ions including C$_{5}$H$_{6}^{+}$ and C$_{5}$H$_{5}^{+}$ that dominate the dissociation channels at low energies ($<$25 eV) are observed. Ar$^{+}$ charge-transfer reaction with QC produces C$_{5}$H$_{5}^{+}$ and C$_{7}$H$_{7}^{+}$ as the major ionic species. Some selected hydrocarbon ions, i.e., C$_{3}$H$_{3}^{+}$, C$_{5}$H$_{3}^{+}$, C$_{5}$H$_{5}^{+}$ and C$_{5}$H$_{6}^{+}$, which are formed from QC by electron ionization, are found to react with QC forming C$_{7}$H$_{7}^{+}$ and C$_{7}$H$_{8}^{+}$ as the major product ions, while the latter two ions are unreactive with QC. The relative rates of the hydrocarbon ion reactions, compared to the Ar$^{+}$ charge-transfer reaction, are rather low; while the rate for C$_{3}$H$_{3}^{+ }$is less than 20 percent of the Ar$^{+}$ reaction rate, the rates for C$_{5}$H$_{3}^{+}$, C$_{5}$H$_{5}^{+}$ and C$_{5}$H$_{6}^{+}$ are less than 3 percent.