MEASUREMENTS OF THE KINETIC-ENERGY RELEASED IN DECOMPOSITIONS OF PROTON-BOUND DIMERS OF PRIMARY AMINES

The kinetic energy release (KER) associated with the decomposition of protonated dimers into the protonated and neutral monomer has been mea sured for a homologous series of primary monoamines, primary diamines, monobasic cu-amino acids and dibasic cc-amino acids by linked scans ( B-2/E) on a two-sector instrument and by mass-analyzed ion kinetic ene rgy spectroscopy (MIKES) on a four-sector instrument. The T-0.5 values were between 16.1 meV and 26.1 meV for the linked scans and between 1 0.3 meV and 17.7 meV for the MIKE spectra. For the protonated dimers o f monoamines and monobasic amino acids, the KER of the decomposition i ncreases with the number of degrees of freedom of the ion. For the pro tonated dimers of diamines and dibasic amino acids, the KER of the dec omposition reaction is independent of the number of degrees of freedom . This difference must reflect a difference in the potential energy su rfaces across which the decomposition of the two types of protonated d imers takes place. There seems to be a tendency of KER for decompositi on of the proton-bound dimers of primary amines to fall with the proto n affinity (PA) of the neutral within an isomeric series. This indicat es a correlation between the PA of the amine and the critical energy f or decomposition of the protonated dimer. For the protonated dimers of monoamines, the results are in agreement with the assumption that the reaction occurs without a barrier for the reverse reaction.