Electron ionization of 1,3-cyclohexadiene and 1,4-cyclohexadiene

Electron ionization of the two cyclohexadiene isomers has been found to produce similar ion populations with comparable total cross sections. The total cross sections for 1,3-cyclohexadiene and 1,4-cyclohexadiene were measured to be at maxima of 1.42 × 10−15 and 1.41 × 10−15 cm2, respectively, at 80 eV. Results show that the major product ions are the four largest ions, C6H5–8+, with combined intensities contributing more than three quarters of the ion populations. Minor product ions include C5H3,5+, C4H2–6+, C3H2,3,5+ and C2H3+. The branching ratios for the major product ions from the two isomers match each other well at low energies near thresholds but differ slightly at elevated energies; while the branching ratios for the minor ions are approximately identical between the two isomers within error limits.