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.
PAC, 1991, 63, 1541. 'Recommendations for nomenclature and symbolism for mass spectroscopy (including an appendix of terms used in vacuum technology). (Recommendations 1991)' on page 1550 (https://doi.org/10.1351/pac199163101541)