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: M + XH^+ → MH^+ + X. The symbolism [M + H]⁺ may also be used to represent the protonated molecule. The widely used term 'protonated molecular ion' to describe the MH⁺ ion is not recommended, since it suggests an associated product of a proton with a molecular ion.