An ion formed by interaction of a molecule with a proton abstracted from an ion, as often occurs in chemical ionization according to the reaction: \(\rm{M}+\rm{XH}^{+}\rightarrow \rm{MH}^{+}+\rm{X}\). The symbolism $\ce{[M + H]^{+}}$ may also be used to represent the protonated molecule. The widely used term 'protonated molecular ion' to describe the $\ce{MH^{+}}$ ion is not recommended, since it suggests an associated product of a proton with a molecular ion.