Ion Formation by Electron Capture

When a neutral molecule interacts with an electron of high kinetic energy, the positive radical ion is generated by El. If the electrons have less energy than the IE of the respective neutral, El is prohibited. As the electrons approach thermal energy, EC can occur instead. Under EC conditions, there are three different mechanisms of ion formation [65,75-77] 

Resonance electron capture directly yields the negative molecular ion, M , whereas even-electron fragment ions are formed by dissociative electron capture and ion-pair formation. Molecular ions are generated by capture of electrons with 0-2 eV kinetic energy, whereas fragment ions are generated by capture of electrons from 0 to 15 eV. Ion-pair formation tends to occur when electron energies exceed 10 eV. [77] 

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