Writing Conventions for Molecular Ions

Electron ionization mainly creates singly charged positive ions by ejection of one electron out of the neutral. If the precursor was a molecule, M, it will have an even number of electrons, i.e., be an even-electron ion (or closed-shell ion). The molecular ion formed upon El must then be a positive radical ion, M , i.e., an odd-electron ion (or open-shell ion). 

Definition The molecular ion has the same formula as the corresponding neutral molecule. The neutral and its molecular ion only differ by one (or more) electron(s). A singly charged molecular ion can either be a positive radical ion, IVE, or a negative radical ion, hT (not in the case of El). ITie nominal mass of this ion corresponds to the sum of the masses of the most abundant isotopes of the various atoms that make up the molecule [5,6]. 

Note The symbol IVT does tiot mean one added electron. The radical C) symbol is added to the molecular ion only to indicate the remaining unpaired electron after ionization. Addition of one electron (electron capture) to a neutral would make it a negative radical ion, M . 

When initially formulating the ionization process, one did not consider where the charge would reside (Chap. 2.2.1), e.g., for methane we wrote  

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