Mass Spectrometric Observation of Electron and Proton Transfer Reactions between Positive Ions and Neutral Molecules. Part II

Abstract

The method of Cermak and Herman has been applied to studies of unsymmetrical charge and proton transfer reactions. If the charge is transferred between atoms low cross sections are observed since part of the kinetic energy of the reacting system has to be converted into internal energy of the reactants. Large cross sections, however, have been found for the charge transfer between polyatomic species where apparently no resonance restriction exists. In several instances the unsymmetrical transfer B++A ➝ B+A+ has a higher rate than either of the processes B++B or A++A. If the ionization potential of B is lower than that of A the cross sections are in general low. In certain cases exceptionally large cross sections are observed and can be explained by the excess energy of a long lived excited state of the donor B+. Dissociations following the transfer of one charge from a doubly charged ion to a neutral molecule such as Kr+++H2O ➝ (Kr+)*+ (H2O+)* ➝ OH++H , NO+++NO ➝ (NO+)*+(NO+)* ➝ N++O have also been observed. The results indicate that the doubly charged ion generally captures the electron into a high lying orbital. Protonated cyclopropane is shown to be readily formed in ionized cyclopropane. In mixtures of water and methane, proton transfer has been observed in both directions. A large isotope effect on the secondary ion currents resulting from the transfer of a deuteron or a proton has been found in several simple systems. This isotope effect appears only if the secondary ions are observed in the Cermak—Herman method and is not found in the conventional operating of the ion source where reactions of slow ions predominate. This information provides some insite into the mechanistic details of the proton transfer since little isotope effect is expected if the reaction occurs via an inelastic collision complex while an isotope effect of the order of magnitude observed here is predicted by a stripping model.