Ion–Polar-Molecule Reactions: Energy Dependency of Hydrogen Atom and Ion Transfer in the Methanol–Acetaldehyde System

Abstract

A tandem mass spectrometer has been employed to investigate hydrogen atom, hydrogen ion, and charge transfer in collisions involving specifically deuterium-labeled methanol and acetaldehyde and their molecular ions at energies between 1 and 7 eV (laboratory system). At the lowest incident ion energies, hydrium transfer is preferred from the electronegative group, while randomness is approached at higher energies. Ion transfer is the most important process at all energies, and transfer of the hydrogen ion from the electronegative group is always favored. The nonrandomization of equivalent atoms in a possible complex suggests that the ion retains its identity in the reaction. Both the atom and the ion transfer show a marked isotope effect. These results are interpreted by charge localization in the reactant ion and a direct mechanism in which long-range forces are important.