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

Kinetic and thermodynamic isotope effects on the unimolecular dissociation of proton bound dimers were studied in the gas phase using mass spectrometr y techniques. In addition proton transfer reactions were investigated using equilibrium techniques in conjunction with a theoretical study. Normal iso tope effects were observed for all of the amine systems studied. The effect of label position, extent of labeling, size and structure of the proton bo und dimers have been discussed with respect to (i) the kinetic and thermody namic isotope effect on the dissociation reaction, (ii) the kinetic energy release on the dissociation reaction, (iii) the thermodynamic isotope effec t on the proton exchange reaction between the labeled and unlabeled amines, and (iv) the effective temperatures and the excess energies of the metasta ble proton bound dimers. Other compound classes (CH3OH, (CH3)(2)O, CH3CN an d (CH3)(2)CO) were studied and discussed in the same way, though not as tho roughly. AU the systems show normal isotope effects, except for the proton bound dimer of CH3CN and CD3CN, which showed an inverse isotope effect. (C) 1999 Elsevier Science B.V.