Electron-impact dissociative ionization of fluoromethanes CHF3 and CF4

The electron-impact dissociative ionization of fluoromethanes CHF3 and CF4 has been investigated by probing their supersonic expansions with a beam of electrons of selected kinetic energy within a time-of-flight mass spectrometer system. Partial (absolute) ionization cross sections of all the nascent ions arising from electron impact, namely CF3+, CHF2+, CF2+, CHF+, CF+, HF+, F+, CH+, C+, and H+ from CHF3 and CF2+, CF22+, CF3+, CF32+, CF+, C+, and F+ from CF4, were measured for electron incident energies up to 100 eV (nominal). The kinetic energy distributions of the nascent ions were also characterized and the information that they supply combined with the appearance potentials (APs) provides an improved identification of the molecular dissociative ionization channels. The correlation between the channel AP and the character and energies of the precursor molecular orbitals is discussed.