H–D exchange at low energy in a collision cell between protonated aromatic hydrocarbons and D₂O, CD₃OD and C₆D₆

H–D exchange reations which occur between protonated molecules (mainly aromatic hydrocarbons) and deuterated neutrals (D 2 O, CD 3 OD and benzene‐ d 6 ) were studied using a hexapole collision cell. The efficiency of exchange is dependent on the proton affinity difference between aromatic and target molecules but the pattern of deuteration in the exchanged ions does not change as might be expected with collision gas pressure. The incident ion energy also has only a small effect on the pattern up to a certain value, but above that value no exchange occurs. It is suggested that ions which shows multiple exchange have the same distribution of transit times, independent of collision gas pressure and, within the above limits, of initial energy. The rate‐determining step is then exchange in an ion–molecule complex rather than collision rate.