ion/molecule reaction

in mass spectrometry
An ion/neutral species reaction in which the neutral species is a molecule. The use of ion-molecule reaction is not recommended; the hyphen suggests a reaction of a species that is both an ion and a molecule and is not the intended meaning.
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 1556
Orange Book, p. 206