Isotope effects in dissociation reactions of proton bound amine dimers in the gas phase

Abstract

Kinetic and thermodynamic isotope effects on the unimolecular dissociation of proton bound dimers were studied in the gas phase using mass spectrometry techniques. In addition proton transfer reactions were investigated using equilibrium techniques in conjunction with a theoretical study. Normal isotope effects were observed for all of the amine systems studied. The effect of label position, extent of labeling, size and structure of the proton bound dimers have been discussed with respect to (i) the kinetic and thermodynamic isotope effect on the dissociation reaction, (ii) the kinetic energy release on the dissociation reaction, (iii) the thermodynamic isotope effect on the proton exchange reaction between the labeled and unlabeled amines, and (iv) the effective temperatures and the excess energies of the metastable proton bound dimers. Other compound classes (CH 3OH, (CH 3) 2O, CH 3CN and (CH 3) 2CO) were studied and discussed in the same way, though not as thoroughly. All the systems show normal isotope effects, except for the proton bound dimer of CH 3CN and CD 3CN, which showed an inverse isotope effect.